selection handler.

Merge master to master-vs-deps

Merge master to master-vs-deps

Merge master to master-vs-deps

Merge dev16.1-preview1-vs-deps to master-vs-deps

Merge master to master-vs-deps

Merge dev16.1-preview1 to master

Merge dev16.1-preview1 to dev16.1-preview1-vs-deps

Properly pass along cancellation token when calling OOP service during FAR.

Move Powershell formatting to match arcade

* Implement pattern-matching in the nullable walker

Fixes #29909
Fixes #31881
Fixes #30952
Fixes #33499
Fixes #30597
Fixes #32414
Fixes #23944

* Remove infinite recursion by using an empty struct cache.

* Changes per code review comments.

* Remove debugging code accidentally left behind.

* Analysis of patterns-matching in the nullable walker requires valid (>0) slots.

* Skip a flaky test

* Patch after merge.

* Make ctor private to force use of factory methods

* Correct a typo.

* Fixup after merge.

Fix Mono crash

Fix inverted condition in LegacyCompletionCondition

Merge master to master-vs-deps

Merge dev16.1-preview1-vs-deps to master-vs-deps

Merge master to master-vs-deps

Merge dev16.1-preview1 to master

Merge dev16.0-vs-deps to dev16.1-preview1-vs-deps

Merge dev16.1-preview1 to dev16.1-preview1-vs-deps

Two space indent is an abomination but it's the standard that Arcade
chose. Moving our Powershell to be consistent with the standard.

Merge remote-tracking branch 'origin/dev16.1-preview1-vs-deps' into merges/dev16.1-preview1-to-dev16.1-preview1-vs-deps

Merge remote-tracking branch 'origin/dev16.1-preview1-vs-deps' into merges/dev16.0-vs-deps-to-dev16.1-preview1-vs-deps

Be smarter for how we raise WorkspaceChange events when completing batches

* move StreamJsonRpc to 2.0

* use object and collection initializer

* changed to throw rather than return

* share JsonRpc creation when it can share code

* add linked files to share code

* more moving around so that we can have linked file working

* addressed PR feedback

* changed name to WatsonReporter

* moved to latest streamjson version

* added a way for partner to add thier own json converter to roslyn service hub service base type

* fixed test break.

it is caused by behavior changes between StreamJsonRpc 1.x and 2.x

* added comment follow PR feedbacks

* updated comment following feedbacks