Also fix the IDE helper to get value usage info, which fixes the MakeFieldReadOnlyAnalyzer

Fixes #29373
Fixes #30175

update Optimization data to 2.11.0-beta1-63312-03

* Calculate CompilerArtifacts in a target

Calculating the set of files in evaluation phase is incorrect, since it depends on files of dependent projects to be copied to output directory.

Don't mark Microsoft.CodeAnalysis.Elfie as a private package

This is a package we depend on via normal means, and expect it to
be referenced in our NuGet packages as they are today.

Merge dev15.9.x to dev16.0.x

Revert "Fix #30091 throwing exceptions"

This reverts commit b3ac2a6f.

Merge dev15.9.x to dev16.0.x

The general pattern when registering code fixes seems to be
either passing diagnostics[0] or diagnostics.First().

RemoveUnusedVariable seems to be the only outlier in this case,
doing .Single().

Having multiple diagnostics on a span would cause the code fix
to throw an exception

Add support to save current tools options into an .editorconfig file

default to vsn if NGenApplication is not set

Add test for Span not allowed as lhs of ??=

This ports https://github.com/dotnet/roslyn/pull/28472, that went into the `editorconfig-ide` feature branch, into `dev16.0.x` branch with following additional refactorings/enhancements:

1. Generated .editorconfig file has all localized string as comments.
2. No hardcoding of individual options in the editorconfig file generator. Instead, each `EditorConfigStorageLocation` now requires to provide a delegate to convert a given option value into the .editorconfig string representation (basically complimentary of the parsing delegate that was already required).
3. Introduce concept of `OptionGroup` to enable grouping options in the same feature (such as CodeStyleOptions, CSharpCodeStyleOptions, FormattingOptions, CSharpFormattingOptions, etc.) into sub-features or groups (such as "this. preferences", "expression-level preferences", etc.). This enables the editorconfig generation to group the related options, without explicit knowledge of each option group.
4. Expose `AllOptions` from each option feature (such as CodeStyleOptions, CSharpCodeStyleOptions, FormattingOptions, CSharpFormattingOptions, etc.), so that the corresponding `IOptionProvider` always stays in sync with implemented options.

Fixed IntelliSense suggestion for read-only class properties in object initializers 

Merge dev15.9.x to dev16.0.x

`InternalError` and `InsertMethodWithExplicitInterfaceSpecifier` were
both added with ID "80", but in different release trains.

`InternalError` was created as "80" for 15.9, so therefore we really
shouldn't change that as it would _definitely_ break SQM/telemetry/etc.

`InsertMethodWithExplicitInterfaceSpecifier` was created as "80" for
16.0, which hasn't officially shipped yet, so I'm changing that one to
"81". Now, that does mean any incoming SQM/telemetry/etc. will conflate
these for any interal builds of 16.0, but that's the least problematic
solution I could come up with.

Looks like that's not quite fixed yet. Disabling and seeing if I can get
this failing locally.

Issue #29660 continues to track this area

(cherry picked from commit 5d9af1f4)

fix embeded type issue

Merge features/compiler

* dotnet/dev16.0.x: (512 commits)
  Sign CoreXT packages (#29986)
  Some more minor refactoring per feedback
  Address PR feedback and also handle few more cases identified during dogfooding: 1. Bail out for explicit interface implementations for properties, we only did so for methods. 2. Bail out for types with StructLayoutAttribute 3. Conservatively handle member references inside DebuggerDisplayAttribute argument by doing a simple string contains check.
  Change RemoveUnusedMembersAnalyzers to be a non-Style analyzer
  Fix issues identified during dogfooding.
  Create AddAwait refactoring (#28930)
  Address PR feedback (use static ctor and remove regions) and also fix an assert seen during dogfooding.
  Enable DeadCodeAnalysis rules and address design/review feedback.
  Disable VSTHRD010 to improve build performance
  Disable procdump since it prevents FailFast event logging
  Log information about crashes during integration tests
  Move xunit package references to Roslyn.Toolsets.Xunit.targets (#29664)
  Fixed a missed save
  PR feedback
  Fix race in SourceParameterSymbol
  Add option keywords to enable searchability (#29764)
  GenerateDeconstructMethod code fixer (#28286)
  Fix race in SourceEventSymbol.GetAttributesBag
  Switch to Arcade targets for building VSIXes (#29590)
  Add Make Field Readonly test for accessed fields
  ...

Fixed langversions