Merge dev15.7.x to dev15.7.x-vs-deps

Document the use of lazy initialization in TargetFrameworkUtil

Make HostAnalyzerManager a bit lazier

Enable building sourcebuild

Merge dev15.7.x to dev15.7.x-vs-deps

Avoid creating all metadata references in the TargetFrameworkUtil static constructor

Avoid IForegroundNotificationService interaction from tests that can't use it

Fixes #25930

Merge dev15.7.x to dev15.7.x-vs-deps

We take the analyzer references provided from VSIX extensions and create
a map of AnalyzerReference.Id -> AnalyzerReference, which is done by
cracking the metadata and getting the .NET assembly identity for them.
We were doing this on the UI during package load, which really isn't
necessary.

While implementing the tests for the ref-reassignment test plan (#22466)
I found a bug in the handling of the ref-escape scope of a ref local in foreach. That bug is fixed
and the rest of the items in the test plan should have a test.

Fixes #22466

* Produce errors on invalid pdbpath supplied to compiler

* More tests

The scenario listed in https://github.com/dotnet/roslyn/issues/22700
demonstrates the problem. The direct cause of the crash is that local
lowering produces two instances of the lambda and lamda conversions in
the resulting bound nodes. This crashes the closure conversion pass
since the same lambda cannot appear in two places in the tree. However,
even if that were allowed, this would violate the language
specification.

Placing a lambda inside an indexer which is nested in a compound
assignment creates two calls which contain the delegate produced by the
lambda expression. If the expression kind is marked as side-affecting it
will be spilled into a temporary variable. However, the local lowering
doesn't distinguish between whether an expression is side-affecting and
whether or not it is referentially transparent. In this case, both
matter. Since the delegate produced by the conversion can be compared by
reference to any other delegate produced by the same lambda, the code
must be referentially transparent -- it must produce the same result
when evaluated repeatedly.

The fix is small: mark lambda conversions as side-affecting. There are
certain cases, like the creation of temporaries for out-of-order calls
with named parameters, where the lambda conversion is only required to
be non-side-affecting instead of referentially transparent, but it does
not currently seem worth the implementation effort to split up the code
path.

Fixes #22700

Disable flaky test WorkCoordinatorTests.FileFromSameProjectTogetherTest

See #25931

* Overload Resolution now fails with the correct error

* PR Comments

* Clean up

* Partial methods implementation should match declaration parameter ref kinds

* More tests

fix the KnownImageIds.LocalVariable which was missed in the previous PR

use latest language version for Miscellaneous Files workspace

Merge dev15.7.x to dev15.7.x-vs-deps

This moves a few of the patches from sourcebuild into the Roslyn source proper.
We now condition on DotNetBuildFromSource in some of our imports, and ensure
that we're not targeting netframework when building for it. We also add a sln
for SourceBuild, SourceBuild.sln, which includes the minimum projects that it
needs.

Bind ForEachVariableStatementSyntax.Variables for error recovery

Make VBCSCompiler a non-critical process

* Previous PR comments

* Missing tests from test plan

* Enable unmanaged constraint on local functions

* Clean up

* PR Comments

* More tests

* PR Comments