move designer attribute back to document level scanner but made it to use keep alive connection rather than creating new connection every time. also kept some optimization such as checking cps projects or not reporting as much as we can. (#22248)

* IDE Changes

* tests

* PR comments

Fixes #22272

* Add errors for ref-readonly signatures, readonly structs, and ref structs

* EE now working with ref-readonly

* Fix failing tests

* PR Comments

We don't need the split anymore now that we're only supporting Dev15.

Unfortunately this required the introduction of a NuGet package that
has a namespace "Workspace" to our VS project, which meant I had to
disambiguate Workspace wherever it's used in that layer. I considered
doing an extern alias instead to disambiguate, but applying that to a
ProjectReference isn't supported. That's tracked by NuGet/Home#4989.

We were not generating a cached completion item rule for a non-preselected item in a tuple context that was also an alias context
Fixes https://github.com/dotnet/roslyn/issues/22002

In preparation for a merge of features/ioperation to master, we have decided to internalize all the IOperation APIs which are either not tested or not reviewed by the design team.
This includes the following APIs with bugs tracking reviewing/adding tests for them: IArrayElementReferenceExpression(https://github.com/dotnet/roslyn/issues/22006), IAwaitExpression(https://github.com/dotnet/roslyn/issues/22007), ICatchClause(https://github.com/dotnet/roslyn/issues/22008), IEndStatement(https://github.com/dotnet/roslyn/issues/22004), IPlaceholderExpression(https://github.com/dotnet/roslyn/issues/21294), ISizeOfExpression(https://github.com/dotnet/roslyn/issues/21296), IStopStatement(https://github.com/dotnet/roslyn/issues/21297), ITryStatement(https://github.com/dotnet/roslyn/issues/22008), ITypeOfExpression(https://github.com/dotnet/roslyn/issues/22003), IWithStatement(https://github.com/dotnet/roslyn/issues/22005)

This change also includes a simple API rename: IMethodBindingExpression renamed to IMethodReferenceExpression(https://github.com/dotnet/roslyn/issues/21289).

added ability to run OOP in 64bit. currently it is not enabled. but it can be enabled explicitly through options or remotely through a/b testing.

a/b testing is not enabled yet.

Update the 'add named arg' refactoring to support only adding to the current argument (for C# 7.2 and above).

Fixes #21889