Support args for `editor.action.trimTrailingWhitespace` command

[jednano]

• VSCode Version: 1.11.1
• OS Version: Windows 10 Pro

Feature Request

Support 2 additional args for the editor.action.trimTrailingWhitespace command:

commands.executeCommand(
    'editor.action.trimTrailingWhitespace',
    uri,  // (optional, but useful when the doc in question is not within an active editor)
    reason  // (manual, auto-save, etc.), useful for NOT trimming auto whitespace
);