Don't warn about "!", regardless of context (https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-10-29.md).

Closes #30177.
Closes #30021.

Moved C# to not pass multiple children to constructors, and instead just pass the original bound node.

Remove NonNullTypes context and other unnecessary information stored in TypeSymbolWithAnnotations. (#30913)

Remove NonNullTypes context and other unnecessary information stored in TypeSymbolWithAnnotations.

Fixes #30845.

Explicitly handle nullability analysis for unconstraint type parameters.

Related to #29981, #29993

* Move Index from unary operators to a stand alone node

* Remove indexer hack

* Remove prototype comments

* Testing/fixing IDE services

* Added EE tests

* Rename "Index" nodes to "FromEndIndex"

* More comments

* Some minor fixups and test fixes

All known outstanding tests are added. Also addressed all known
outstanding work items.

Also implemented detection of nullability mismatch in constraints for an implicit interface implementation.

CoalesceAssignment no longer considers IsChecked, as it's not necessary
for dynamic in these scenarios.
ICoalesceAssignment is no based on IAssignmentOperation.
Small logic updates as fallout from testing more dynamic conversion
scenarios.

Added support for initial binding, dataflow passes, and the local lowering
pass for null coalescing assignment. IOperation and CFG support will come in
a follow-up PR, as will relevant semantic model testing.

Also adjust the CFG builder and unit tests to account for IOperation tree shape changes.

We now no longer generate ICollectionElementInitializerOperation, and have
obsoleted that interface. In it's place, we now use IInvocationOperation
and IDynamicInvocationOperation for collection initializers.
Additionally, added some tests around missing collection initializer
scenarios.

Additionally updated calcluation of Default and ParamArray parameters in
VB to correctly handle collection initializers, as they previously were
always being detected as ArgumentKind.Explicit.

Ensure that expression variables (improperly) declared in a case expression are captured in bound nodes. (#26918)

* Ensure that expression variables (improperly) declared in a case expression are captured in bound nodes.
Fixes #26896
Note that this fix is temporary, made via changes to code that is deleted in the recursive-patterns feature branch.
The bug naturally won't exist in the C# 8 code base due to pattern-matching changes.

* Add BoundSwitchBlock.Locals for illegal locals.
Note that this is a temporary fix, as this node doesn't exist in C# 8.