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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.

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.

Treat System.Void as the absence of a type.

Fixes #1766.

Fixes #246

Extend Linux CI support

Couple of changes to the scripts:

- Factored out installing the PCL libraries to setup-pcl.sh.  Makes it
much easier to install PCL against custom builds of mono
- cibuild.sh accepts an optional `—os` option now. Makes it easier to
customize Jenkins based on the OS target.

Fixes #1123

Update the ThemeColorFixer to trigger on IClassificationFormatMap.ClassificationFormatMappingChanged. This allows us to update the tooltip classifications when the user manually changes colors or imports color settings.

We previously listened for WM_SYSCOLORCHANGED and WM_THEMECHANGED, but those are now redundant and have been removed.

In some scenarios, an attribute application can be “bad” due to an error type in referenced compilation, but without any diagnostics reported for the referencing compilation.

Added couple tests for ?. operator for cases missed in optimizations.

Test-only change

The tests arep assing, but codegen is not great.

Use msbuild variables for assembly versions of Immutable and Metadata references

This reverts commit 94b22b7c.

The issue was the "DirectCast(Nothing, CompileResult)" (later removed by
commit 90bb89f0).  When compiling without
optimizations, this returns a structure initialized to its default value.
When compiling with optimizations, this throws NullReferenceException.
I've filed bug #2094 for the inconsistency.

Introduce msbuild variables for versions of Immutable and Metadata nuget packages

Retry with System.Core.dll on ERR_NoSuchMemberOrExtension.

Suppress expansion of void* rows

...because they would have type ```void```, which can't be instantiated.

Avoid a hang in CompileWithRetry...

Don't attempt to retry if we're asked to load the same assembly identity more than once.  Adding the same reference won't help anything, and we will almost certainly never terminate the retry loop.

Add support for "dynamic" in the result provider