Fixes #29956

Also introduce a helper `TypeSymbol.IsVoidType()`

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

Merging on behalf of @jnm2

Debug info cannot express reuse yet. Locals backed by reused fields cannot be seen in EE for now regadless of their names.

We currently provide every local with its own proxy, even when locals are in disjoint scopes.
That is done for the purpose of debugging, especially EnC.

We do not have to do this in Release ( /o+ ) and reduce the size of async state where possible through reusing of backing fields.

NOTE: reuse does impact debugging experience when reuse happens - locals that are mapped to recycled fields generally cannot be examined. Otherwise debugging experience stays the same.

Fixes:#15290

Related to #8817, #8814.

Add ability to associate annotations with type symbols exposed by other symbols. For example, with property's/method's return type, parameter's type, etc. As part of this change, custom modifiers are now handled as an annotation.

Fell out of our normal cadence for this during the push for RTM. Now that we
had a bit more breathing room getting us back on track here.

Old: Scopes followed the bound tree, so the outermost scope was within the
try-catch block synthesized in async MovedNext methods.

New: If the entire try block would be a hoisted local scope, we remove the
marker node (BoundStateMachineScope) and insert a new one around the
entire method body.

Upshot: hoisted locals are still in scope when stopped on method closing
braces.