TAW: Check that generated access widener matches expected output

[Juuxel]

See #2695 (comment).

This prevents builds with outdated access wideners when the MC version changes, or when template.accesswidener is modified.

Also simplifies the code a bit - text.lines().collect(Collectors.toCollection { [] }) for getting a mutable list of the lines in a file was replaced with Groovy's readLines extension method wrapped in a new ArrayList for safety.

[modmuss50]

This is a good start, however there are a few modules that have generated TAWs and/or resources. This only covers one module. Running the generateResources task during the github action run and then ensuing that git has no changed files may be an easier way to do this?

[Juuxel]

That's true but needs some more work with the scripting (ofc individually doing my thing for all modules would take more time still) and this can be used locally for validation which is a plus.

I might still PR the clean-ups from here though, no reason to use streams here.