Ensure that we don't execute Initialize and compilation start actions for analyzers with no enabled rules

Fixes #15184

Publish Assets to dev15-rc2 branch

Don't crash during shutdown if we try creating metadata snapshots

Ensure we don't free metadata from under skeleton assemblies

Package loading time improvements

Remove needless subclassing with refactoring providers.

When we create skeleton assembly references, we back them by temporary
memory out of our ITemporaryStorage service. We used a
ConditionalWeakTable to ensure that if the reference was held alive
that the underlying memory wouldn't disappear. This was subtly
incorrect. If you had a PE symbol from such a compilation, the
compilation is not held alive, and the metadata reference could be freed
but the metadata (which is held by the symbol) could still be held.
This meant we'd free the memory too early and crash.

The fix is simple: root the memory by the metadata object, not the
metadata reference.

Fixes #13243.

Merge microupdate into master

Do not crash on cancellation in FindReferences.
Fixes #15113

The definite assignment errors were fixed by changing the design of local functions
to allow forward calls to local functions in scope.

Fixes #13029

Fix NuGet.exe caching

Don't generate a variable if it would conflict with another local in scope.

Fixes #11777

Make FindReferences work in auto-property intializers.

Fixes #10714

add try catch at the first await so that we can get dump at right exc…

Do not run code style analyzers on generated files.

Fixes #12044

add try catch at the first await so that we can get dump at right exception point rather than having it as inner exception

Build updates

Our script for downloading NuGet.exe now ensures the local copy is the correct version.  Previously it assumed any local copy was the correct version.  Lead to problems when we brought down a new version that had bug fixes necessary for building the repo.

h another local in scope.

fixed race where build start event could be fired multiple times.

Merge dev15-rc into master

Show a cancellable wait-dialog when invoking change-signature manually.

Fixes #4891