Fixes https://github.com/dotnet/roslyn/issues/19954 and https://github.com/dotnet/roslyn/issues/20125

Fixes #19926

Rename Microsoft.CodeAnalysis.Metadata project to Microsoft.CodeAnalysis.Debugging to match the namespace

Fixes #19927

Remove IUnboundLambdaExpression from IOperation API, return an ILambdaExpression for UnboundLambda nodes.

removed Operation cache. due to how we changed to hold onto child (Lazy(Of T)), we no longer need cache for children for a bound node

and that removes the need to have the old cache

Fixes #19902

Fixes #18300

This is an automated migration of our project files to the new SDK /
PackageReference.  It is done using the tool located here:

https://github.com/jaredpar/ConvertPackageRef

Ensure that we get a well formed child IOperation tree even for bound nodes for whom IOperation support is not yet implemented

This ensures that the analyzer driver/operation walker is able to find all the descendant IOperation nodes within these not yet implemented features. We should remove the IOperationWithChildren interface once we have designed all the IOperation APIs.

TODO: Implement the VB part.

Fixes #8884

Refactored IVariableDeclaration to IVariableDeclarationGroup, which allows for multiple declared symbols as part of a single declaration.

this doesn't replace or change anything yet, just bunch of Operation types for next step.

next step is creating CSharp/VBFactory which return these Operation type and replace callsite that return bound node with this.

after that, I will create xml/generator from Operation.xml.Generated.cs which can produce Operation.xml.Generated.cs

this is easy step. just spliting all IOperations as its own files and put them in its own folder

* Harden compiler against exceptions during stream dispose

It's possible (likely even) for one of the streams the compiler uses for
output files will throw during disposal. Currently this crashes the
compiler. This change adds a wrapper type around stream to catch
exceptions during disposal and report them as diagnostics instead.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems?id=217719

* Add VB tests

* Respond to PR comments

* Respond to PR comments

* Respond to PR comments

* Conform to style guidelines