Add plugin testing workflow

[LastTalon]

Splits up workflow actions into general CI and formatting for clarity. Workflow actions are no longer separated by plugin/extension for because of interaction when reporting coverage (the extension does not yet report coverage).

Includes all necessary config files for testing including:

• .gitignore additions for build and testing artifacts
• .luacov for coverage testing
• separate rojo projects for building and testing
• foreman.toml for dev and testing tooling
• testez-companion.toml (we can run tests on ourself!)
• testez as a submodule shared between the build and tests
• Lemur and Roblox test runners for CI testing

[LastTalon]

The failing coverage reporting is normal when no tests were conducted. The workflow should be good for review now.

[LastTalon]

Just figured out prettier had been overriding my tab settings in json files (with no config file). The formatting should be consistent now.