Fixes some issues with code formatter

[kapilmb]

Fixes the following issues:

• If the user switches the active editor when code formatter is running, the formatter can write to the new active editor.
• If the user executes "format document" on a document when the document is already being formatted, the extension creates a redundant request for formatting the same document.
• If for any reason PSES crashes, then the formatting status is not cleaned up from the status bar.

[daviwil]

Sweet, thanks!

[kapilmb]

Thanks @daviwil!