Constrain availability of ref conditional expressions to language versions 7.2 and higher

Fixes:#24306

Update string text for keybindings reset.

* make sure OOP inherit same culture as VS otherwise culture sensitive resource such as xml doc comment will not work properly

* don't crash on expected issue

Fix a case where the stack spiller spills more than needed. (possibly resulting in false errors)

* dotnet/dev15.6.x:
  Fix symbol completion after 'in' (#24335)
  use PascalCase for const name
  Limit compiler server pipe name length (#24265)
  Test ConvertedType on LHS of deconstruction-assignment (#24158)
  remove unused usings
  use .editorconfig files
  address more comments
  address code review comments
  move newly added text into resource file
  add text and hyperlink to C# code style page

Add a link to Tools>Options>…>Code Style to link to EditorConfig documentation. Bug#23513

On MacOS pipes are implemented using Unix domain sockets. Unix domain
sockets must have a valid file path for their endpoint. The best place
is in the temp folder. Unfortunately, domain sockets on Unix also have a
very small path length limit of 104 characters. In addition, Mac temp
paths can be very long since they include randomly generated characters
from the OS. In total, this means that Roslyn has barely 50 characters
worth of space for its pipe identifiers.

This change cuts down on the bytes of the SHA256 hash used. This shouldn't
affect the security of the pipe, since the hash isn't used as a security boundary,
but should fit the pipe name into the length limitations.

Fixes #24137

Move to xunit 2.3.1

The new analyzer warnings are valid but are quite noisy. Going to
suppress them for now to unblock this upgrade. Will fix them in a
separate change.

VB does not have this particular bug and corresponding scenario works correctly.
There are however other bugs beyond the scope of what is fixed in this PR.

* moved waiter from diagnostics.dll to features.dll where all interfaces are defined.

* simplified listener and waiter and moved those in product.

* cleaned up a bit

* fixed some comments

* forgot to add new AsyncListenerProvider in test export composition

* fixed dead lock found on unit tests

* remove all waiters left

* added dispatcher event processing in one more place

* added a way to enable waiter through env variable in test such as DDRIT

* added env var support so that It can be used without internalvisibleTo us.

* dont wait for all waiters but only onces each test used to wait.

* removed dependency to Roslyn.Services.Test.Utilities in integration test. that dll is not in probing path.

* fixed test failures

* fixed bug in integration tests

* move call to enable waiter before creating workspace so that workspace event queue get proper async listener

* expose concret type as well so that it can be directly used in test for waiter

* addressed PR feedbacks.

* rename mess up

* extra ) left out

* fixed build failure

The last await-containing expression in an argument triggers spilling of all argument before it.
The value of the expression itself, however, should not be spilled. (there are no awaits after it)

Agreesive spilling may result in substandard codegenration and/or unexpected errors.

* Simplify diagnostic tagging by making it use the standard tagging model.

* Cleanup.