Enable preview SDKs for CI builds

this particular code path can take a long time if metadata reference hasn't created its symbols yet.

this can get really bad if we try to show code lens for something like IDispose.Dipose and it tries to create all metdata references in the solution.

since it is not cancellable, just passing by a Dipose method can cause this to occupy CPU 100% for several seconds and there is no way to make it go away.

now we pass in cancellation token so that we can bail out  sooner.

Disable TypingHelpDirectiveWorks for legacy completion

GetWriteTaskAsync often completes synchronously

Add support for .editorconfig files to MSBuildWorkspace

support retries in integration tests

This test is flaky in legacy completion, but legacy completion is slated
for removal so the test failures were not fully investigated.

Remove prebuilts during source-build

Our CI machines don't have a new enough MSBuild to support this; adding
it is tracked by https://github.com/dotnet/core-eng/issues/6424 which
is currently underway but there's no reason to hold up the larger
work on the test.

* Write Roslyn assembly version to DependentAssemblyVersions file

* Depend on GetAssemblyVersion to ensure AssemblyVersion has been calculated

* Update implicity declared type expression nullability:
- When updating the implicit type in a declaration also update the bound type declaration nullability
- Record nullability for inferred foreach variable
- Add nullable public api tests
- Add nullable tests

Implement generate method and constructor with top-level nullability tracking wrapper

* mark NFW from OOP critical

currently, whenever OOP throws an exception, we show infobar saying "restart VS". whenever that happens, we report NFW. now those NFW will be marked as critical and we will stop reporting NFW after that in VS.

basically making critical NFW behavior same as fatal watson in VS. and management will treat critical NFW same as fatal watson.

also, now we will show callstack like code fix exception when info bar is shown

* xml document fix

* fix build break.

* changed button to hyper-link to follow same pattern as other info bar (code fix)

show remote exception in callstack view.

* introduced enum for Watson Severity

DisposableWaitAsync often completes synchronously

Pass CancellationToken instead of CancellationTokenSource

Avoid captures in SqlConnection.ReadBlob

Update AnalyzerRunner to support IIncrementalAnalyzer testing

* Learn from comparisons to non-constant, non-null values

* Update comment

* Remove unused local function

* Remove another unused local function

* Check for null constant before trying to learn from notNull == maybeNull. Add tests

* More tests, more cleanup

* Add conditional access with || test

* More test updates from feedback

* Cleanup

* Change some locals in tests to parameters

Update FindImplementationsForInterfaceMemberAsync to correctly handle ambiguous type returns (#35853)

FindImplementationsForInterfaceMemberAsync checks for forwarded types using SymbolFinder.OriginalSymbolsMatch, which expects non-null compilation for both the project containing the interface and the project containing the symbol to compare to. Until now, most instances have found equivalence without falling through, but in cases where the type forwarding isn't completely verified a non-null compilation for the interface symbol is needed as well. See VerifyForwardedTypes for the logic being used.

In #35786 the type System.Text.Encoding is provided by a a NuGet reference and could be ambiguous based on the build target. The OOP service attempts to find the correct type resolution but needs the original symbol compilation to verify.

Without this fix, FindAllReferences may cause a null deref and fail.

Fixes #35786

* Update ILAsm and ILDasm version to match expected SDK version

* Fixed version numbers

This makes the extension method work again. The workaround is tracked by
https://github.com/dotnet/roslyn/issues/36093.

This catches places we're calling Construct() or
ClassifyConversion().