Merge #2981

Merge #2981

2981: vscode: Add ability to call onEnter without overriding "type". r=matklad a=71

Before this PR, the only way to get enhanced typing (right now, only with `onEnter`) was to override VS Code's `type` command. This leads to issues with extensions like [VsCodeVim](https://github.com/VSCodeVim/Vim) that need to override `type` as well.

This PR adds an additional command, `onEnter`. This command can be used with the following keybinding, which allows the user to get smart `onEnter` behavior without overriding `type`.

```json
{
    "key": "enter",
    "command": "rust-analyzer.onEnter",
    "when": "editorTextFocus && editorLangId == rust"
}
```

Co-authored-by: Gregoire Geis <git@gregoirege.is>
Co-authored-by: Grégoire Geis <git@gregoirege.is>