Properly show defaults for value types in sighelp

Add test demonstrating issue is fixed.

Fix issue where we were not offering to simplify

Move UsePatternMatching 'is' and 'as' analyzers/fixers/tests to shared layer

Have the formatter properly group usings as per user option (and only when applicable).

Fix add-local-variable formatting.

Fix race in doc comment provider.

Port AddAccessibilityModifiers analyzer/fixer/tests to shared layer

* Add support for MemberNotNull/When attributes

* Fix overflowing test

* MemberNotNull on override and with try/finally

* Fix regression

* Update tests

* Honor MemberNotNull on overrides

* WIP on enforcement

* Warn on referencing member from base type

* Cleanup

* Resolve conflicts

* Fix inheritance, PE and property scenarios

* Fix a test

* Address feedback from Neal (on NotNullWhen)

* Fix more scenarios with try/finally

* Fix analysis of split invocation

* Fix bootstrapping issues

* Add test

* Apply MemberNotNull on calls with instance receivers

* Check reachability instead

* Handle staticness mismatch

* Resolve merge conflict

* Address 2 remaining comments

* Fix another merge conflict for bootstrapping

* Add tests and fix assertion crash

* Fix generate file

* Use struct instead of tuple

Add feature to simplify trivial boolean expressions.

Do not add 'new' when there is no conflict in implement-interface.

Add test demonstrating issue is fixed.

Move designer attribute scanning out-of-process