This reverts commit 646489a3.

* Build color schemes into pkgdef resources

* Add files to read items from PKGDEF files

* Apply ColorScheme PKGDEF as defaults colors

* Add ColorScheme dropdown to Advanced Options page

* Update formatting for contributed PkgDef files

* Add margin to custom theme warning

* Address ColorApplier feedback

* Updated based on PR feedback

* Change to a VsixColorCompiler package that includes VC runtime

* Remove VsixColorCompiler

* Move native methods

* Remove PKGDEF reading

* Add additional color options to ColorSchemeOptions

* Add color scheme reader for reading the scheme XML

* Add coverter for turning color schemed into registry entries

* Update applier to read schemes from xml

* Initialize applier on package load

* Update option pages to refresh onLoad

* Remove VsixColorCompiler PackageReference

* Implement feedback from Code Review

* More feedback from Code Review

* Update file headers

* WIP

* Resolve PR feedback

* Use SchemeName in place of name strings

* Fix options persistence

* Make OptionChanged event nullable

* Revert change to GlobalOptionService

* Revert to using VisualStudioWorkspace for accessingOptions

1. Make the strings sentence cased
2. Rename "Open Documents And Projects" to "Open documents" as per internal review.

Revert "Switch the error list scope combo box to match the newly selected background analysis scope in Tools Options."

This reverts commit be5bd275.

Switch the error list scope combo box to match the newly selected background analysis scope in Tools Options.

Address PM feedback and change the user facing resource strings to match the error list terms in its scope filter combo box

`Active file` -> `Current Document`
`Open files and projects -> `Open Documents and Projects`
`Full Solution` -> `Entire Solution`

Replaces the existing "Full Solution Analysis" option, with a background analysis scope to allow users to control the analysis scope for all solution crawler based background analysis.

Fixes #38429. Active file scope minimizes all the background analysis to the active files, saving on CPU consumption from background analysis on remaining files in the solution.

I have also updated up the low virtual memory listener which detects low VM and used to turn off just the full solution analysis to now set the background analysis scope to "Active file" for the current session.

Fixes #38051: Users can now use this command to force complete all the analyzers on a project/solution (includes NuGet based + VSIX based analyzers, including IDE code style analyzers).
Complements #39544: Users can now potentially disable continuous analyzer execution  during live analysis and instead execute them on demand with these commands.

Few things to note:
1. This change hooks up new "Run Code Analysis on ProjectName" menu commands for CPS based managed projects. These commands are already hooked up for csproj based legacy projects in StanCore, but that should eventually go away.
2. This change only hooks up these new commands for top level Build and Analyze menus. Adding these to "Analyzer and Code Cleanup" context menus for project/solution in solution explorer is much trickier as the command groups are defined in StanCore. I will do so in a separate PR.
3. This change also exposes a "RunAnalyzers" API for StanCore, so we can trigger analyzer execution when user executes run code analysis on solution/csproj based project. There is a VS side PR that will consume this functionality to make the experience uniform across all "Run Code Analysis" commands.

At this point, the nullable support in the semantic model seems stable,
and there's no reason for somebody to manually turn this on since any
project that is using nullable will turn it on automatically.

Revert the functionality to show info bar to make editorconfig a solution item for existing solutions with existing editorconfig

1. IDE code fix that adds new editorconfig for configuring code style/severity has been updated to create the file at root of the solution, instead of the project. Additionally, the code fix also automatically adds the file as a solution item.
2. We now detect if user opens a solution with editorconfig at the root of the solution and provide an info bar to make it a solution item with a single click. User can choose to silence this suggestion for the current solution (solution user option) OR silence it for all solutions for the user (workspace option).

* Both columns added

* Genericize custom column names

* More changes to genericize

* Cleanup

* Respond to feedback

* WIP

* Change tuple to properties

* Restrict to just containing types

* Cleanup

* cleanup

* Refactor

* Change method for getting Containing Type and Member

* refactor GetAdditionalProperties

* Fix merge conflicts

* respond to feedback

* respond to feedback

* Change to struct

* Add type for AbstractCustomColumnDefinitionWithMultipleValues

* Cleanup

* Change AdditionalProperty to FindUsagesProperty

* respond to feedback

* respond to feedback

* Hide columns in F#

* respond to feedback

* fix merge conflict

* Change from hiding columns to removing columns for non supported langs

* Add additional implementations

* formatting

changed our task center status bar to say "low priority background process" rather than "live analysis" to reduce confusion on what "live analysis" means since term "live analysis" has strong association with "errors" in VS.

also, it now shows ## of pending work and whether BG process is paused or not.

Hook up the configure severity context menu commands and functionality from a context menu in error list that shows up when a diagnostic entry is right clicked. For now, we allow configuration only if a single configurable diagnostic is selected. In future, we may allow bulk selection and configuration (IMO that doesn't seem like a very useful scenario, unlike bulk suppression from error list where individual diagnostic instances are suppressed).

At this point, the flighting controls we have aren't really useful
anymore: we want this on for everybody unless the opt out, and that
opt-out would be specific to certain users that are running into issues
with the new system to keep them unblocked. I'm keeping this a per-
machine setting (that doesn't roam) because it's really repo or VS
version specific.

Addresses part of https://github.com/dotnet/roslyn-analyzers/issues/2023

This PR converts our current experimental feature that recommends installation of [FxCopAnalyzers VSIX](https://marketplace.visualstudio.com/items?itemName=VisualStudioPlatformTeam.MicrosoftCodeAnalysis2019) into a non-experimental feature that recommends installation of [FxCopAnalyzers NuGet or VSIX](https://docs.microsoft.com/en-us/visualstudio/code-quality/install-fxcop-analyzers?view=vs-2019).
All the experimental checks have been removed, but I have retained all the existing logic about when the infor bar shows up (light bulb invoked on 3 separate days for separate VS sessions).