Add dependencies between Swixproj

Merge dev15-preview-4 into master

The Swixproj projects encapsulating each Vsix should mention the
dependencies betweeen them similar to the dependencies stated in the
contained Vsixes.

Refactor completion insertion

Remove unnecessary override.

Object creation providers don't need to compute insertion text.

Fixes #11812 

Remove unneeded parameters.  Simplify data passed in completion.

Avoid resolving symbols at insertion time.

Always insert the insertion text, even when we can't resolve symbols.

Fixes #12254

Fix command line parsing of quoted values

Add extra logging to invocation of ibcmerge...

Add partial-type-name suggestions to C# and some fixes for VB

Merge dev15-preview-4 into master