* Add example that reports diagnostics

Extract test helper GetDefaultDiagnosticAnalyzerService()

Fix failure to apply timeout in WaitForAllAsyncOperations

Fix crash when typing in an indexer.

File header cleanup

Closes #46487

* Update TestRunner.cs

* Update TestRunner.cs

Closes #43258

Change GacFileResolver.IsAvailable to check a type from System.Core

Fix failures to use VBCSCompiler.exe for Roslyn builds

Fix improper construction of DiagnosticAnalyzerService

Add a new command line switch to skip analyzer execution

See #46684

Finish 'Generate Equals' conversion to new test library

Add restricted IVTs for IntelliCode

Fix couple of issues related to SerializableOptionSet which were leading to checkum validation asserts

* Expose generator internals:
- Add a new api + result objects to return generator driver internals
- Rework the way we handle exceptions, especially for syntax walk based operations
- Ensure we don't mix up generator and driver exceptions

Null annotate SymbolKey and a bit more of the compiler

Add integration test to configure diagnostic severity via editorconfig

Stop specifying Rich Nav's version of dotnet

Delete our use of Microsoft.VisualStudio.CodingConventions

Fixes #40926

This support was added to `Microsoft.CodeAnalysis.targets` (ships with VS) in VS2019 16.5:
https://docs.microsoft.com/en-us/visualstudio/code-quality/disable-code-analysis?view=vs-2019.

However, the MSBuild property is not respected from 'dotnet' builds where this targets file is not imported (see https://github.com/dotnet/roslyn/issues/40926#issuecomment-574506716 for details).

This change moves the skip analyzers logic down to `Microsoft.Managed.Core.targets` and core compiler layer so it is respected for all builds. As per offline discussions with Jared and Chris, we can no longer skip analyzer execution from MSBuild by removing the "Analyzer" items as these can include source generators, which should never be skipped (at least there are no current scenarios where we want to skip generators). Hence, we are adding a new command line compiler switch `/skipAnalyzers`, optionally followed by a `+` or `-`, to allow skipping analyzers.

I verified the end-to-end functionality works fine by locally building `Microsoft.Net.Compilers.Toolset.Package` NuGet package and referencing it in a project.

Combine local and LSP code action logic

Move C# editorconfig diagnostic support API to CompilationOptions, instead of SyntaxTree