Self host vbc builds on Mac CI

Port CA1027 and CA2217 (Mark\Do not mark Enums with FlagsAttribute) to S...

 Port CA2213 (Disposable fields should be disposed) to System.Runtime.Analyzers

PropertySymbolKey considers indexer metadata name

Use an unmanaged stream during PDB writing

This updates our cibuild.sh script to include self hosting the VBC
build in addition to the CSC build.

The support is limited to our Mac runs only for the moment due to Linux
not being upgrade to the proper mono runtime.   This will be updated in
the near future.

Cross Platform build issues

Fixes internal bug #916341

Update PropertySymbolKey.Resolve to consider the metadata name of
indexers. Prior to this change, resolving regular properties considered
the metadata name but resolving indexers did not. Checking the metadata
name for indexers is important for distinguishing between explicit
interface implementations.

More improvements to the ?. codegen.

Include pseudo-variables in CompileGetLocals

Invoke SetAdditionalFiles on compiler inputs when initializing from msbu...

Invoke SetAdditionalFiles on compiler inputs when initializing from msbuild csc task fails and we fall back to initializing from model. This should fix the local unit test failures in MSBuildWorkspace additional file unit tests that some developers are hitting.

Better handling of unary operators (like:  - foo?.Bar  )
Better lowering strategy for nullable receiver - we no longer rewrite to a ternary ?: in such cases which leads to more optimization opportunities.

Fix recursion problem in syntax normalizer

Show C# snippets with no SnippetType

Update ApplyChangesOperation doc comments

Trigger ThemeColorFixer on FormatMappingChanged

Introduce a CodePage1252Encoding class

Encoding.Default is not available on CoreCLR and neither is Encoding.GetEncoding(1252). So we have to roll our own.
Fixes #2081 

Fixes internal TFS bug #1156267. The behavior now matches that of Visual
Studio 2013.

Fixes a number of cross platform build issues:

- Managed tools which run as a part of build are now prefixed with
`mono ` in a standardized fashion.  This is now uniformly applied to
all tools for generating bound trees, syntax nodes, etc …
- Remove WPF references from TestUtiliites.csproj.
- Used reflection to access the GetRuntimeInterfaceAsObject API as it
is unavailable in the Mono APIs.

Script updates

Do not allow private members to be referred to in cref across assemblies

Do not crash when highlighting alias symbols defined via global imports.

Keep track of “bad” attribute applications to prevent PE generation in their presence.

Fixes #1904

Don't recommend #Const after #Const

Allow directive keyword recommenders to differentiate between the start
and middle of a preprocessor directive.

Fixes #722.