Fixes:#22306

* Create tests to cover test plans #19216 and #20127

* clean up

* Improve consistency of handling constant null switch expression
Fixes #20210
* Rationalize reachability for pattern switch.
If a single case could handle all inputs, e.g. has the
same constant value, a wildcard pattern, etc, then
the default label is considered unreachable.
The concept of reachability, which takes the value of the
switch expression into account and can produce warnings,
is separate from the concept of subsumption which takes
the full set of patterns into account and can produce errors.
* Document breaking change in pattern switch.
Alse change formatting as suggested in code review.

Fixes #22378

Fixes #21515

* IDE Changes

* tests

* PR comments

Tests in response to issue #22253

Fixes issue 21801

Merging on behalf of @alrz. Thanks

Ref ternary shoudl be shielded form optimization in the containing expression that may expose it to mutations

Just need to add it to the list of other possible writeable lvalues checked by WouldBeAssignableIfUsedAsMethodReceiver helper.

Fixes:#18220

Improve method type argument inference around tuples and address backwards compatibility break. (#22295)

Fixes #20583.

Fixes #21297 and #22004

- makes val escape switch comprehensive (unhandled/unexpected nodes will cause an exception)
- tests for added expression kinds
- handle varargs correctly in the escape analysis + tests

Fixes #22272

Ref-readonly locals are mostly identical to ref-readonly parameters. The
most important difference is that when possibly mutating methods are
called on ref-readonly locals of struct type, a proper temporary is
created before calling the method.

* ported tests from https://github.com/dotnet/roslyn/pull/21263

* added ref readonly test

* added more tests following PR suggestion

Fixes #22265

TypedReference
ArgIterator
RuntimeArgumentHandle

Fixes:#https://github.com/dotnet/roslyn/issues/22198