Merge telemetry sources into existing projects

Now that the telemetry API is consumable from OSS and the code is there, no
need to have a dedicated binary + vsix for it.

Share refactoring code between C# and VB.

Merge dev15-preview-4 into master

Do not go back to the symbol to determine what text we will insert for a completion item.

Support doc comments for symbols declared off an anonymous type.

Fixes #12530

Refactor how we do completion item insertion.

VisualBasicSyntaxFactService shared default instance.

Support async methods returning Task-like types

[Based on features/async-return with tests ported from that branch.]

Remove unnecessary resource.

Respect filter flags when searching for symbols.

Fixes #12169

[Based on features/async-return with tests ported from that branch.]