Set up PMD Code Analyzer

[aidnem]

Set up the PMD static code analyzer using the gradle plugin, as documented here.

[godmar]

I enabled id "pmd" in the plugins section of the 2025 Robot Code base, which would pull a default version of PMD. I wasn't too impressed with the results, although it did flag many of the cases where you guys checked in commented-out code that led to unused variables and/or assignments.
The generated .html file wasn't nicely integrated with vscode; I couldn't figure out how to click on a line to get to the code.

Separately, I installed "PMD for Java", a vscode extension by cracrayol. This gave me a different set of errors, so it must have been a different version of PMD than the gradle plugin.

Both versions flagged a number of things we'll probably want to suppress per general rule.

[aidnem]

@godmar thanks for trying this out. While this obviously isn't an optimal solution for those of us who don't use vim, I found that moving your cursor over a path in normal mode and typing "gf" works for file links in text files. I'm not sure if you can open the HTML file with VSCode easily, but that would at least be better than nothing.