Add TS Server command for 'add all missing imports'

## Search terms - code action - source action - Add missing imports - getCombinedCodeFix ## Feature request Add a new TS Server command that triggers 'add all missing imports' for a given file. ## Use case VS Code allows users to [configure code actions that are run on save](https://code.visualstudio.com/Docs/languages/javascript#_code-actions-on-save). One of the supported code actions is `source.addMissingImports` which attempts to add all missing imports in a file. Users can also setup keybindings for these specific actions To implement this, right now we request all code actions for the file and then try fetching the 'add all missing imports' combined fix for one of them. This is complicated and results in the TS Server doing extra work. It would be better for us if we could ask the Typescript server: give me the edits that add the missing imports in this file