Expression attributes fail

[brendt]

This is with the Vue plugin disabled:

Demo code: https://github.com/tempestphp/tempest-plugin-demo/blob/main/app/home.view.php

[xHeaven]

Part of this issue should be solved via #40.
Actually recognizing variables will need a different fix.

[xHeaven]

#44 will fix template variables (eg. {{ $book }}) that are typehinted with PHPDocs, but won't fix built-in attributes (eg. :foreach, :if) yet.