Merge dev16.0-preview2 to master

Remove NonNullTypes context and other unnecessary information stored in TypeSymbolWithAnnotations. (#30913)

Remove NonNullTypes context and other unnecessary information stored in TypeSymbolWithAnnotations.

Fixes #30845.

Explicitly handle nullability analysis for unconstraint type parameters.

Related to #29981, #29993

Merge dev16.0-preview2 to master

Set master prerelease version to beta3

Fix up our build badges

Implement new interfaces for adding files

Merge dev16.0.x to dev16.0-preview2

Fixes https://github.com/dotnet/roslyn/issues/30966
Implements the spec change described in https://github.com/dotnet/roslyn/pull/30670
See also https://github.com/dotnet/roslyn/issues/30989

Remove unused method SerializableBytes.CreateReadableStream

Fix Edit and Continue in CPS projects

Adds support for testing parsing to the compiler benchmark suite and
refactors the whole suite to make it smaller and simpler.

Add bunch of exclusions to dead code analysis for special methods

The problem was our CPSProject type no longer was implementing the ENC
interfaces the project system expects; this copy/pastes the same code
over that's being used for AbstractLegacyProject.

Merge dev16.0.x to dev16.0-preview2

Adding new training data and updating training scenarios

Merge dev16.0-preview2 to master

Unused members analyzer: Do not flag write-only properties that are n…

Add csharp_prefer_braces to .editorconfig

Merge dev16.0.x to master

Workaround in RemoveUnusedMembersDiagnosticAnalyzer for VB handles cl…

Fix IndexOutOfRange exception in InvocationExpressionSignatureHelpProvider

Fixes #30886: Bail oun special serialization constructors and methods with certain special attributes indicating special usage.

Fixes #30887: Bail out on ShouldSerializeXXX and ResetXXX pattern that was also excluded from legacy FxCop implementation and seems to be common in real world code.

Fixes #30377 : Bail out on methods with signature matching event handlers, which are very common in Web apps.

Allow VisualStudioExperimentationService to initialize on a background thread