Merge master into dev15.1.x

Fix parameter syntax

Fixes #14146

Allow specification of a test search directory

Ensure package is loaded by loading CPS project

Capture better dumps for DevDiv #363724

Duplicate some existing scoping tests for pattern declarations in declarator arguments, where they are not permitted. (#16804)

* Duplicate some existing scoping tests for pattern declarations in declarator arguments, where they are not permitted.
Fixes #13660

Remove space preventing editorconfig settings from applying to vb files

Downgrade SyntaxVisualizerExtension dependencies

Bump the NuGet moniker to -rc5

We've shipped -rc4 packages to nuget.org, so any future builds should
be versioned higher.

Capture better dumps for https://devdiv.visualstudio.com/DevDiv/_workitems?id=363724&fullScreen=true&_a=edit

Very infrequently, ImplementsClauseCompletionProvider is asked to provide symbols with a null context. It's not clear why this would happen. Add a FatalError.Report if we try to call any provider with a null context.

Merging on behalf of @DanMcNultyDev

Add test coverage for Out Vars in global code in remaining executable statements.

Added test to verify intellisense on Enumerable.Join parameter types

Closes #14113.

More pattern matching scope tests

Prevent error on Analyzer project creation

this change prevents an error on RC.3

Add test binding redirect for System.Xml.XmlDocument

changed all caller to call JsonRpc.StartListener once all states are set

Gather better info when AddDeclarationConflictsAsync crashes

Avoid deadlocks when unloading unloading multitargeted Asp.NET projects, or .NET Standard (CPS) Projects (directly or via Solution close) referencing Shared Projects

capture document on findtoken crash in linked files

We are seeing reports of Visual Studio crashing in FindToken with argument out
of range exceptions.  It appears that this is causes by linked files being of
differing lengths.  This change captures the original and linked documents
on the stack so we can better understand what is happening.

Fix crash in roundtripping a symbol that references a LocalFunction's TypeParameter.

Fix VisualStudioWorkspace thread affinity and defer creation

Avoid deadlocks when unloading .NET Standard Projects (directly or via Solution close) referencing Shared Projects

Fixes https://github.com/dotnet/roslyn/issues/14479

The problem here is that unloading projects takes a serialization lock,
which can cause Shared Project IVsHierarchys to notify us that their
context hierarchy has changed. In response to this, we try to set the
new active context document for open files, which also tries to take the
serialization lock, and we deadlock.

For .NET Framework Projects that reference Shared Projects, two things
prevent deadlocks when projects unload. During solution close, any
Shared Projects are disconnected before the projects start to unload, so
no IVsHierarchy events are fired. During a single project unload, we
receive notification of the context hierarchy change before the project
is unloaded, avoiding any IVsHierarchy events if we tell the shared
hierarchy to set its context hierarchy to what it already is.

Neither of these behaviors are safe to rely on with .NET Standard
projects, so we have to prevent the deadlock ourselves. We do this by
remembering if we're already in the serialization lock due to project
unload, and then not take the lock to update document contexts if so
(but continuing to lock if it's not during a project unload).