Delete the checkbox to control nullable analysis in the IDE

Live Share - Support Empty Workspace

LSP Server Handle DisplayTextPrefix and DisplayTextSuffix on Completion Items

Move optimization around use of Nullable type in Boolean Expressions into LocalRewriter and eliminate invalid optimization. (#38802)

* Move optimization around use of Nullable type in Boolean Expressions into LocalRewriter and eliminate invalid optimization.

Fixes #38305.

The goal of optimization is to eliminate the need to deal with instances of Nullable(Of Boolean) type as early as possible, and, as a result, simplify evaluation of built-in OrElse/AndAlso operators by eliminating the need to use three-valued Boolean logic. The optimization is possible because when an entire Boolean Expression is evaluated to Null, that has the same effect as if result of evaluation was False. However, we do want to preserve the original order of evaluation, according to language rules.

* Fix an old bug masked by #38305.

* Fix an old bug masked by #38305.

* More fixes fo old bugs masked by #38305, plus optimizations that wouldn't be performed by compiler.

* PR feedback

Fix minor issue in IfToSwitch refactoring

At this point, the nullable support in the semantic model seems stable,
and there's no reason for somebody to manually turn this on since any
project that is using nullable will turn it on automatically.

Move much of local function data flow to AbstractFlowPass

Remove dead class diagram

Move to renamed analyzer utilities package

Switch some calls to ThreadHelper.ThrowIfNotOnUIThread to something else

Merge release/dev16.4 to master

Fixes an issue in CFG where we incorrectly handle using declarations that fall under labels. It follows a similar pattern to how we handle lowering in the local re-writer.

Fix an assert in IOperationExtension.GetValueUsageInfo

It seems there's a flaky issue in our unit test setup where sometimes
ThrowIfNotOnUIThread will throw even if you're on the JTF main thread.
It appears the implementation relies on checking the Dispatcher object
that must sometimes not be set up right. We have a standard mechansim
anyways for asserting that we are on the UI thread that consumes our
IThreadingContext, so switching the helper we call should avoid this.

The URI path parsing is not the same as Windows path parsing and
sometimes produces incorrect results. However, a canonical Windows
path should produce an equivalent URI. This change uses GetFullPath
for absolute paths passed to the ErrorLogger to normalize the path
before passing it to URIs. For relative paths we try to normalize
the directory separators, but there's no equivalent transformation
that guarantees correctness.

Fixes #37737

Handle declaration pattern parented by switch expression arm in GetValueUsageInfo.
Fixes #38640

Include severity values when generating preferred modifier order EditorConfig options