Add automation text for the PreviewPane we show in Lightbulbs

changed behavior of LastDesignTimeBuildSucceeded following suggestion…

made open file only analyzer to run properly for fix all and suppression.

Enable NuGet debugging

Re-enable IBCMerge on workspaces

Temporarily enable NuGet debugging to help NuGet team track down a debugging issue.

Use the correct treatment flight name for analyzer A/B test

Fix for #18978 Cast is redundant on call to params method

FindRefs not cascading to interface impls with structs.

changed behavior of LastDesignTimeBuildSucceeded following suggestion on https://github.com/dotnet/roslyn/issues/19626

Build Roslyn against 15.3

Merge dev15.3-preview2 to master

When the baseDir is not specified GitLink attempts to probe for the .git directory.
This probing is done by looking at the first source file it finds in the PDB and
walking upwards.  This is a bit of a flawed strategy because generated files in
our Obj directory get referenced in the PDB but don't necessarily need to be in the
cone of the .git directory.

Fixing this by just being explicit about our Git directory.

https://github.com/GitTools/GitLink/issues/155

Change our GitLink invocation code to use on of our standard process spawning helpers.  Currently looking at some
potential bugs in our source server support.  Want to eliminate a potential corner case that our old error handling
could have hidden.

Build Roslyn against 15.3

Ignore tuple name and dynamicness differences in computing constant value for as operator on nullable tuple (#19697)

Also updates other references based on Preview 1 and moves from
Microsoft.Composition to System.Composition

Changed the code comment mentioning "null literal" and "special case" and replaced it with a more general description.

tweak how we merge build and live errors for language such as F#

Be resilient to options being serialized as strings.

Don't offer to convert to pattern matching when type is nullable.

Enable TestPreviewDiagnosticTaggerInPreviewPane.