Fix Incorrect links in "vscode namespace API" Doc

Introduce a backup file model inside IBackupFileService

Make cmd+k clear terminal on Mac

Fixes #12585

Issue #15610

**bug**
For implicit js/ts projects that trigger the large project warning in vscode, the action currently tries to create a jsconfig.json file in `/dev/null/...`

**Fix**
In cases where the `jsconfig.json` file returned by tsserver is not under the root worspace, create an empty `jsconfig.json` at the root of the project instead.

Remove the node-additions typings file and changes the semver typings to come from `@types/semver`.

 In description for ExtensionContext -> storagePath, links to globalState and workspaceState are incorrect and lead to an error page.

fixes #15796

Contributable dirtydiff 

Reference counted (workbench) text models