Tweak completion filtering behavior. #2

#1. made persisted storage exclusive to 1 process. like before, second VS with same solution will not use persisted storage.
#2, tweaked sqlite to share cache between connections like esent.
#3, made VS and OOP to use different db files (we can make them to share if we want to, but for now, nobody requires it so we create 2 different db)

..

made OOP mock to enable persisted service.

…struction

Fix issue where a write wasn't detected in make-readonly #2

changed code fix part to use "fix all" and only fixes P1 list rather …

…et#30870)

* Fixing WhenKeywordRecommender to understand var pattern
* Using block body for test methods
* Adding a comment

merge