Fixes #28684.
Fixes #29837.
Fixes #30001.
Fixes #30052.
Fixes #30054.
Fixes #30068.
Fixes #30072.
Fixes #30178.
Fixes #30220.

Merge 'upstream/dev16.0.x' into 'features/NullableReferenceTypes'

'features/NullableReferenceTypes'

Formatting analyzer

Merge features/async-streams to dev16.0.x

Add fallback to MSBuildProjectLoader when project reference is not backed by metadata reference

in the situation where DebugType is mising and the DebugSymbols property is set to true, the TryGetValue method of the s_debugTypeValues dictionary would throw an exception

In MSBuildWorkspace, there's a fair amount of logic to resolve the metadata references that are passed to the compiler
to project references that are defined on the project. This change adds a fallback in the case that a project reference
can't be matched to one of the metadata references. This is primarily a situation where something is wrong with the project
in it's current configuration. For these cases, MSBuildWorkspace will still attempt to add a project reference but also report
a workspace diagnostic. In addtition, this change removes and reports diagnostics for any unresolved metadata references
passed to the compiler after the reference resolution step occurs. In addition, this change exposed a small bug when
ReferenceOutputAssembly is specified for a project reference, which was caught by an existing test and fixed.

Add IOperation/CFG support for VB ReDim statement

Fix exception thrown in MSBuildWorkspace when opening multi-targeted project that references an F# project

Tweak test assertions to be bit more resilient to .NET Core SDK changes which result in TFMs rolling forward

In MSBuildWorkspaceProjectLoader, there is a map of "discovered" projects that stores the results of any project references. If a
project reference can't be loaded (for example, because it is a reference to, say, an F# project), it can end up in the map twice if the
project referencing it is multi-targeted. For example, a multi-targeted C# project that references an F# project will fail when loaded
because the path to the F# project will get added twice with an empty array of ProjectInfos. The reason for this is that the code assumes
that the loaded project will end up in the primary loaded project map, but in this case, the project couldn't be loaded and isn't there. To
avoid this situation, we call TryGetValue on the "discovered" projects map and return the results before trying to load the project again.

Added AddMissingImport CodeRefactoring driven by PasteTrackingService

Added PasteTrackingService that handles the paste command and track
paste information for documents. This paste information can be used
by refactorings to make suggestions based on what was pasted.

Fixes #10272

Do not remove parentheses from incomplete expressions

Update to vs-threading analyzers 15.8.168

See #30264

Report AD0001 if an analyzer accidentally provides a null descriptor …

Fix symbol end action not completing for symbols with non-implicit me…