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

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

* EE now working with ref-readonly

* Fix failing tests

* PR Comments

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

Fixes #21889

Fixes #11489

See #8627

Fixes #11490