Update Kotlin to K2, and other dependencies

[FWDekker]

Updates Kotlin to the new K2 compiler, updates the IntelliJ plugin to the new v2, updates a bunch of smaller dependencies, bumps the compatible IntelliJ version, and does some minor cleanup in build scripts.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.46%. Comparing base (73557f1) to head (e6effe7).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #542      +/-   ##
==========================================
+ Coverage   80.40%   80.46%   +0.06%     
==========================================
  Files          51       51              
  Lines        2087     2068      -19     
  Branches      357      357              
==========================================
- Hits         1678     1664      -14     
+ Misses        338      334       -4     
+ Partials       71       70       -1     

[FWDekker]

Actually, I just realised I didn't update to the K2 compiler. The rest is true, though!