We compile using the alwaysStrict flag so these directives are not needed

This part removes most `use strict` directives that are right after the file header

make tabCompletion be 'on' | 'off' | 'onlySnippets', only compute word end key when tab completion is enabled

* Build VS Code using TS 3.0

Fixes #57151

* Disable snippits in extension search (when not in suggest dropdown)

* Add monaco input contributions

* Fix bug preventing snippetSuggestions from taking effect in sub-editors

Changes unused variables to be faded out instead of greyed out. Add a new theme color `editorUnnecessaryCode.opacity` that controls the alpha for this fade

Fixes #51152