* Update sln/csproj for generated ioperations
* Extract BoundMultiple[Using/Local]Declaration into an abstract base node
* Update VariableDeclarationGroupOperation for UsingDeclarations
* Implement CFG for using declarations
* Update and add tests

There are a few parts to this change:

1. Ensure that MSB3270 and MSB3277 warnings are promoted to errors in CI
and hence block merging.
1. Move our DiaSymReader.Native logic into a separate targets file.
This resource cannot be consumed with a simple package reference but
rather requires a package reference and custom logic to pull out the
contained binaries. This logic used to be spread through our build. Now
it's in a single place.
1. Remove the x86 bootstrapping logic. This was testing a pretty obscure
scenario and the cost of maintaining that logic is siginificant at this
point. Can bring back if we ever find a bug in this area.

The root cause of the MSB3270 warnings is a subtle change in the SDK. It
now passes the runtime graph to NuGet for native assets. In the case of
DiaSymReader.Native there are runtime specific assets hence the SDK /
NuGet had to pick one for framework projects. This eventually lead to
`PlatformTarget` being set to x86 where it shoud have been AnyCPU.

Part of the change includes adding `ExcludeAssets=all` to the package
reference which means they no longer figure into this logic and hence
the binaries are marked as AnyCPU.

This regression in behavior is being tracked by
https://github.com/dotnet/sdk/issues/3495

There are a few parts to this change:

1. Ensure that MSB3270 and MSB3277 warnings are promoted to errors in CI
and hence block merging.
1. Move our DiaSymReader.Native logic into a separate targets file.
This resource cannot be consumed with a simple package reference but
rather requires a package reference and custom logic to pull out the
contained binaries. This logic used to be spread through our build. Now
it's in a single place.
1. Remove the x86 bootstrapping logic. This was testing a pretty obscure
scenario and the cost of maintaining that logic is siginificant at this
point. Can bring back if we ever find a bug in this area.

The root cause of the MSB3270 warnings is a subtle change in the SDK. It
now passes the runtime graph to NuGet for native assets. In the case of
DiaSymReader.Native there are runtime specific assets hence the SDK /
NuGet had to pick one for framework projects. This eventually lead to
`PlatformTarget` being set to x86 where it shoud have been AnyCPU.

Part of the change includes adding `ExcludeAssets=all` to the package
reference which means they no longer figure into this logic and hence
the binaries are marked as AnyCPU.

This regression in behavior is being tracked by
https://github.com/dotnet/sdk/issues/3495

Closes #35071

Roslyn.Compilers.VisualBasic.Test.Utilities.Desktop incorrectly added in a70cdce6
VBCSCompilerPortable removed in b2bd77b0
Microsoft.CodeAnalysis.CompilerServer removed in b00224e7
Roslyn.VisualStudio.Test.Utilities.Next renamed in e0e16d7a
Microsoft.CodeAnalysis.Scripting.Destkop.UnitTests never existed (typo)
Roslyn.DebuggerVisualizers removed in d7e49395
Microsoft.VisualStudio.LanguageServices.VisualBasic.UnitTests never existed (typo in 7ab3b776)
Roslyn.Services.Editor.CSharp.UnitTests2 renamed in bb1f97b6

See #35071

Roslyn.Compilers.CompilerServer.UnitTests removed in 24721202
Roslyn.Test.Utilities.CoreClr removed in cf58bbcb
Roslyn.Test.Utilities.Desktop removed in cf58bbcb
Roslyn.Compilers.CSharp.PerformanceTests removed in cd333330
Roslyn.Test.Utilities.FX45 removed in b77c5473
Roslyn.Compilers.VisualBasic.PerformanceTests never existed (typo from 3c14b040)
Roslyn.Compilers.CSharp.Test.Utilities.Desktop removed in edd89e4e

Closes #35102

This removes the remaining private reflection code from the compiler and
replaces it with multi-targeting approaches.

Also replaces some unsafe code with Span<T>.

Revert compiler changes and move CustomDataFlowAnalysis and DataFlowAnalyzer types to Workspaces layer.
In order to still get test coverage for this custom dataflow walker from compiler layer's flow analysis tests, these files are linked into the Roslyn.Test.Utilities project, and we execute this walker in the compiler unit test's ControlFlowGraphVerifier.

* NuGet packaging

* Add missing VS package references

* Fix scripts

* Add comment on Workspace.Desktop references with PrivateAssets

* Fix Microsoft.NETCore.Compilers package

* Fix up references

* Build fixes

* Correct OutputPath for package projects

* Use NuGetRepack to force exact versions in per-build packages

Instructions can be found in the README file under src/Tools/CompilerBenchmarks.

This is the same parser used by Visual Studio for editorconfig with a
minor modification to use case-insensitive comparison for property keys.

Implicit framework references were disabled at the time we moved over to
the new SDK due to some remanants of project.json in our build. Those
have all been cleaned up now and hence moving us over to using implicit
framework references.

Not having this enabled meant the API surface we were targeting in our
projects was not actually what was available in the project target
framework. Instead it was the intersection of the target framework and
the set of NuGet packages we reference. This meant that code which
should work simply wasn't due to the API surface not being correct.

This change makes the legacy behavior contingent on the runtime of the
compiler. When the compiler is running on the desktop runtime, the
legacy signing code will be used. When running on CoreCLR, the new
portable signing code will be used. This fixes key container signing for
almost all scenarios (signing using a key container when the compiler is
running on the desktop framework). Signing using a key container on
Windows using a compiler running on CoreCLR is still broken, but that is
a far rarer case.

This change also fixes delaysign, which would full sign the file if the
keyfile passed to the compiler contains a private key.

Fixes #25340
Fixes #25424

Adds System.Threading.Tasks.Extensions as a dependency.