1. Do not flag parameters whose name has not yet been written (empty string). Fixes #36817
2. Do not flag parameters of partial method definition part. Fixes #36816

This reverts commit 0d8d2afb.

If you mouse over a local, field, etc., and we have computed nullable
flow analysis for it, we'll tell you whether the compiler thinks the
item is null or not at that point.

Fix couple of unit tests that started failing after #36566 merged from master to release\dev16.3-preview1

Not sure why the unit test failures were not caught by the merge PR, as these tests are failing consistently in CI for PRs targeting release\dev16.3-preview1

Related to #35619.

Conflicts:
	src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs

set "DeferUntilIntellisenseIsReady"=dword:00000000 for csharp and VB editor so that we opt out from VS waiting for solution load to complete

make sure we only create OB when VS is running in IDE mode. all command line mode (and all its variations) we don't need to create OB

* Correctly report nullability of tuples in the semantic model:
- Store the original tuple literal rather than just its type
- Visit the original literal without diagnostics only in the nullability walker to understand its type
- Update the generator to allow force visiting fields in the nullable re-writer
- Update type checker to allow checking of converted types too
- Update various tuple tests to be correct
- Add extra tests

This implements IExperimentationService in the remote workspace; any
request for feature flags is forwarded to the main Visual Studio process
and the feature flag is queried there.
Co-authored-by: NJoey Robichaud <jorobich@microsoft.com>
Co-authored-by: NHeeJae Chang <hechang@microsoft.com>

Fixes #36304

Fixes #33464

Workaround for #32100 for Dev16.2

Fixes #34830

Fixes #36715

This slipped through because we didn't have any tests at all for
the case where we are using the type-inferrer to infer the case like:

    a = new A { B = { } }

where the inner one doesn't have a new B before it. The scenario wasn't
new but just happened to be the precise case that was broken.

Fixes https://github.com/dotnet/roslyn/issues/36702

Fixes #30324

razor added new @code block. add support for new code block in roslyn.

for old razor version, IsCodeBlock won't get called since razor will not treat code in @code as C# code block, in new razor version where @code is added, razor will recognize it as C# code block and call us which we will in turn check new @code along with existing @ tags for code blocks.

enabled the nullable feature, either on the command line
or via a nullable enable directive.