Support building the workspaces layer in source-build

Condition targets that use InitializeSourceControlInformation on whether or not that target is available.

Support building the workspaces layer in source-build. Also added a verification step to CI to ensure we don't break the build.

Port the fix for #38183 to 16.3.

Do not report an NFW for analyzer exception diagnostic in IDE

Wire-up to text buffers even if there is no RDT DocDataReloaded

In 735a6532 we stopped listening to
RDTA_DocumentInitialized as a trigger to know when the document might
now be available. We believed it wasn't necessary since DocDataReloaded
would cover it, but files being opened or manipulated via some DTE
interfaces or with the invisible editor seem to still require it.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/937712

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/797080.

We have several Watson buckets that imply that a TypeWithAnnotations structure returned by RetargetingMethodSymbol.ReturnTypeWithAnnotations and RetargetingPropertySymbol.TypeWithAnnotations has null as its Type property. The properties are backed by fields that are initialized by an API that never produces structures like that (with null Type property). I suspect that the situation can arise in case of a race between two threads, where the structure is only partially initialized so that IsDefault check fails in one thread, but the underlying information for the Type property is still not initialized by another thread.

This change eliminates possibility of races like that.

Related to #38247.

Before C# 8, the reduction of an extension method would fail (return null) when the
method's constraints would not be satisfied.  But in C# 8 the unmanaged constraint requires
we know the language version, and therefore the compilation, to check.  That is not available
in `IMethodSymbol.ReduceExtensionMethod`.  So we dropped the constraint checking in #37022.
However this causes an unfortunate regression in the quality of the IDE experience.  So here we
restore the constraint checking, using the compilation's language version when available.
IMethodSymbol.ReduceExtensionMethod uses the C# 8 rules since it has no language version to check.

Fixes #37780

Merge release/dev16.3-preview2 to release/dev16.3

This seems to cause a noticable UI delay while the NFW gets reported. We already report the AD0001 diagnostic with exception callstack and the analysis context on which exception occurred, so user has enough information to file an actionable bug.
Fixes #38180

Merge remote-tracking branch 'upstream/release/dev16.3-preview2' into merges/release/dev16.3-preview2-to-release/dev16.3

Extract method will now maintain nullable reference types for parameters and return types. If the parameters or return types are determined to be non-nullable through flow state analysis, then we will adjust them to be non-null when generating. 

For return type, the adjustment is done after the method is generated. This is because the generator can and will introduce new return statements that need to be analyzed for null state. The only way a return type can be modified to non null is if it:

1. Was null annotated to start with
2. All returns are determined to return non-null by flow state analysis. 

Similarly, reference parameters can be assigned null or non-null values inside a method. We determine parameters can be adjusted if:

1. Null is not passed into the parameter.
2. Null is never assigned to the parameter. 

Remove the 7.3 languageversion from the BindSymbolInOtherFile test

Handle escaping of ref/out parameters on non-regular CFG exit paths (…

Remove inaccessible attributes when generating code

Show nullable annotations in tuple signature help

Update Generate Equals and GetHashCode to handle nullable members

Do not fade code for IDE0016 (UseThrowExpressionDiagnosticId)

Revert test workarounds/skip for IDE diagnostic configuration code fixes

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19419.12

Merge release/dev16.2 to release/dev16.3-preview2

Most of the tests in here still hard code older baselines because they
predate some pattern matching improvements, but this is fully new.

Fixes https://github.com/dotnet/roslyn/issues/37913

Fix generated Equals(object) parameter nullability mismatch

Fixes https://github.com/dotnet/roslyn/issues/37252

Remove RuntimeIdentifiers

Disabling Mono leg

Latest Mono nightly builds appear to have broken serialization during
remoting across AppDomain instances. That is pretty fundamental to how
we test. Temporarily disabling the Mono leg until this can be fixed.

Tracking Mono Issue: https://github.com/mono/mono/issues/16373