Fix a regression in dynamic event addition that would fail at runtime.

Fix projects being removed from the Workspace

Fixes #27006

Fixes #31974
Related to #30655, fixes for C#
Related to #31977, fixes for C#
Fixes #31858

We were leaving them in the workspace by accident.

Fix and validate compiler extension VSIX

Hide the start page to improve test performance

Fix .NET Core project tests

Add code fixer to add [Obsolete] attribute on code that gets an 'obsolete' warning.

Fix QuickInfo tests

This DLL was missing and is a dependency of other DLLS that we put into
this extension.

Use VsShellUtilities to open a file in design view

Merge features/recursive-patterns into master

Publish NuPkg as artifact

Add IVT adapter assemblies

This change replaces the use of DTE with VsShellUtilities.OpenDocument
for opening a file in design mode.

Integration tests now ignore error list entries not associated with a
project, since these entries should have been cleared when the solution
closed.

This workaround should be removed when #32121 is resolved.

Closes #18996
Closes #19090
Closes #19091

Merge master into features/recursive-patterns

Closes #19914

Merge branch 'features/recursive-patterns' of https://github.com/dotnet/roslyn into rpatterns-mergeQ

- Adds further IOperation nodes for recursive patterns: IDiscardPatternOperation, ISwitchExpressionOperation, ISwitchExpressionArmOperation
- Follow-up to #31967 per #32012
- Issue #32012 also describes additional open issues to be addressed later.
- Update compiler test plan.
- Also revert some changes accidentally checked in to the patterns branch.

For each reference that doesn't have an .XML doc file we allocate and cache a FileBasedXmlDocumentationProvider that throws a first-chance exception upon first use.

Add and use a singleton NullXmlDocumentationProvider instead when the requested .XML doc file doesn't exist.

* Fix additional newlines being added when adding all missing imports

* Use syntax formatter to remove extra newlines when adding missing imports

* Apply suggestions from code review

* Added assert to ensure we retain the final newline

* Updated the assert to include cases where a newline pre-existed

Consistently parse .editorconfig option values containing spaces