Get a basic slow acceptance test cases working for testing TS Plugin

[machty]

This issue used for tracking as part of a GH Project

Until Volar 2.5 drops mid-Nov with better support for testing TS Plugins, need to build out a few acceptance test cases with the purpose of testing diagnostics/codefixes/etc that originated from the TS Plugin form of Glint.

As of Jan 10 2025, Volar is still on 2.4 and there has been no forward momentum on Volar providing test infrastructure for TS Plugins, which means we'll need to start building tests for TS Plugins via slow acceptance tests.