* moving methods around to clean things up.

* more clean up

* added comment

* more code re-arrange

* revert some clean up back since that requires some changes I dont want to do for clean up

Delete VisualStudioSetup.Next

Branchless codegen for lifted nullable operators

Add additional information about the found and expected character, when there is an unexpected difference. (#25296)

 Not offering UseAutoProperty for volatile fields & when field used with ref

Fixes #17261

Merge dev15.7.x to master

Adding missing completion after 'ref'

Fixing async keyword highlighting on local functions

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

Merged on behalf of @skynetv 
Thanks

Fixing NullReferenceException inside GenerateTypeCodeFixProvider when System.Action is missing

Trivial fix for potential null-ref in test helper

Bug fixes in SwitchStatementHighlighter

See #25931