* added partial load mode feature flag and made extract method to handle partial load mode.

when solution is opened in VS, currently we do not know when exactly solution is fully loaded or not. solution explorer might show all files but design time build might not have finished yet so, any semantic operation such as extract method or rename might do wrong thing since it doesn't know that it is dealing with missing information (solution).

we are trying to address this issue with partial load mode, new API platform is working on. basically, we are planning to block most of semantic operations (except completion/quickinfo/goto definition/signature help and navigate to. we might include FAR here as well) during partial load state.

also, for things like squiggle, LB and etc, we will disable those until solution is fully loaded since we don't actually know whether those data is correct or not during partial load state.

this change add featureflag so that we can incrementally add support for each features while dogfooding behavior across partners. as a first attempt, extract method is choosen for new experience.

other internal options are added so that we can try alternative behaviors and etc.

test is not added yet.

* fix merge break

* update string

* small tweak.

* PR feedbacks

* updated the title

* updated after discussing about PR

* do even cheaper version of getting text.

addscope doesn't work with description with blank line when scope is nested. wait dialog seems supporting only 2 lines.

until, I figure out this with platform team, making description one line.

* following PR feedback

* Simplify some names in the nullable reference types feature
- Rename `TypeSymbolWithAnnotations` to `TypeWithAnnotations`
- Rename its type field from `TypeSymbol` to `Type`
- Fields of Symbols that are of type `TypeWithAnnotations` that are currently named `Type` would be renamed `TypeWithAnnotations`
Fixes #33736

* Further updates

* Fix formatting

* Add `Type` property in addition to `TypeWithAnnotations`
e.g. `ReturnType`, `ElementType`, etc.

* Post-merge fixup.

* Report nullability for attribute arguments:
- Add an entry point to nullable walker for attribute analysis
- Implement analyze attribute in the walker
- Update MethodThisParameter to not throw
- Add extra fields to BoundAttribute that are needed for nullable analysis
- Add tests



* PR Feedback:
- Analyse attributes even when we don't bind a constructor

- Add tests for when we don't bind constructor but still want to analyze what we have

* PR Feedback:
- fix typos
- make no matching constructors use implicit constructors

* Replace tabs with spaces

* Fix failing test

Report nullness warnings for nullable collections in foreach.

Write the targets files into the correct directory for VS2019

Record which packages were missing if we skipped an installed instance

Move to MSBuild 16.0

Fixes:#31503

Complete statement: special handling needed for caret at end of line, outside of delimiters (#33883)

* Fixes 33851

* Add test

* Fix comment

This is a necessary pre-req to us adotping the 3.0 .NET Core SDK.

[master] Update dependencies from dotnet/arcade

Fixes #33446

Merge master to master-vs-deps

- fix typos
- make no matching constructors use implicit constructors

- Analyse attributes even when we don't bind a constructor
- Don't assume we have a method symbol in enter parameters
- Add tests for when we don't bind constructor but still want to analyze what we have

- Move attribute nullable check to GetAttribute rather than bind attribute

- Change MethodThisParameter
- Clean up nullable checks
- Extra tests

- Don't do analysis for speculative attributes
- Manually call TryGetThisParameter, rather than MethodThisParameter which can throw

- Add an entry point to nullable walker for attribute analysis
- Implement analyze attribute in the walker
- Remove the analysis from binder_attributes and call nullable walker instead
- Add extra fields to BoundAttribute that are needed for nullable analysis
- Add some extra test scenarios

- Support supression
- Fix params array of null
- Fix arguments out-of-order

- At binding time check both constructor and value arguments for const null
- When arguments are arrays, check for nullable array mismatch
- When arguments are non nullable arrays check for nullable inside initializers
- Add tests

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19162.7

* Update dependencies from https://github.com/dotnet/arcade build 20190308.5

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19158.5

* Update dependencies from https://github.com/dotnet/arcade build 20190309.2

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19159.2

* Update dependencies from https://github.com/dotnet/arcade build 20190310.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19160.1

* Update dependencies from https://github.com/dotnet/arcade build 20190310.2

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19160.2

* Update dependencies from https://github.com/dotnet/arcade build 20190311.14

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19161.14

we want to move to newer version of JsonRpc (2.x) from 1.x we use.

but that has some complexity since version 2.x and 1.x is incompatible and we let partner to directly access Rpc exposed from ServiceHubServiceBase type.

this is first step so that partners move to new API that doesn't expose JsonRpc directly.

once they moved, moving us to new versino should be easier since we will not break partner teams.

Fixing false unresolvedConflict when renaming overloaded VB properties

If you are missing a package in your install, we wouldn't say which one
was missing so you got to figure it out the hard way. This will now
log it so you can fix your install.