e.g. `ReturnType`, `ElementType`, etc.

- Rename `TypeSymbolWithAnnotations` to `TypeWithAnnotations`
- Rename its type field from `TypeSymbol` to `Type`
- Fields of Symbols that are of type `TypeWithAnnotations` that are currently named `Type` would be renamed `TypeWithAnnotations`
Fixes #33736

* Address minor issues identified in review #32431.
Fixes #32807

Fixes #32290 
Fixes #32169 
Fixes #32141 
Fixes #32025 

Allow locals, parameters, range variables inside a lambda to shadow names outside the lambda (#32754)

* Expression tree reflike checks WIP

* Move test from emit to semantics

* Fix ExpressionTreeRefLikeWalker

* Fix label indent

* Add more tests

* Move ExpressionTreeRefLikeWalker logic to DiagnosticsPass

* Resolve TODOs in IsExpressionTree

* Ignore BoundConversion when checking for ref structs in expression trees

* Comment on the purpose of `!(node is BoundConversion)`

* Add ErrorCode.ERR_ExpressionTreeCantContainRefStruct

* Use new error code in DiagnosticsPass

* Update tests

* Add TypedReference tests

* Replace IsByRefLikeType check with IsRestrictedType() check

* Simplify VisitLambda

* Add new diagnostics to ArglistTests.ExpressionTreeTest

This updates our duplicate reference check to compare names in addition
to reference identity. This found ~600 tests which were inadvertently
passing duplicate references to our compilation helpers.

closes #25509

Merged on behalf of @svick Thanks!

This unifies our API naming convention. When standard is in the name
then we are using the netstandard2.0 API set and when it is not then it
is the simple desktop mscorlib46.

Both variants are necessary for CompileAndVerify style functions because
many of our tests that use it can only run on desktop or simply need to
have some of the netstandard2.0 API set missing.

MemberSemanticModel.GetBoundLambdaOrQuery should use GetAdjustedNodePosition helper to ensure proper handling of zero-length tokens at the beginning of a syntax node. (#24049)

Fixes #23883.

* Rename Foo to Goo

* Rename ifoo to igoo

* Add back BOMs

Narrow location in diagnostics for lambda symbol to either the delegate keyword or the arrow (#16990)

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems?id=296550.

Fixes #15555
Checking in on behalf of @gafter 

Also added some checks that should help to figure out how to reproduce the crash.

The bug is that, as an optimization, we use 'null' as the delegate type for
a parameterless `delegate` lambda, but code elsewhere in the compiler
assumes that a null delegate type occurs only in error recovery situations.
Fixes #13797

We attempt to bind lambda args against every applicable delegate
type that could be a matching parameter, and then select the
"best" for error recovery.
This also has the effect of removing unbound lambdas from the
bound trees, replacing them with the "best" binding for error
recovery. This makes the semantic model insensitive to any further
trial bindings (i.e. mutation of the unbound lambda cache).
Fixes #12063, #11979, #11901

Remove vestigal "extensionMethodsOfSameViabilityAreAvailable"
thereby reducing coupling between internal compiler APIs.
See also #7740 #5128, where the vestigal APIs were introduced.

While working on another change I noticed that our testing support for experimental features didn't actually verify the underlying feature was experimental.  Hence helpers like ParseExperimental(...) would continue to function without error when tuples / ref returns were attached to the /langver switch.  This creates maintenance issues in our test framework as it's unclear what we're actually testing.

I refactored the code involved to verify the features are actually experimental and removed some troublesome helpers.

Fixes #557, #5498

because there are arguments missing, to force lambda binding
for error recovery.
Fixes #11053, #11358

to ensure that we bind the lambda for intellisense purposes.
I also hand-tested the scenario of #4480 to reproduce it on VS2015
and to verify that the problem does not occur on the master branch.
Fixes #4480