Kate (and now Kdevelop) support LSPs, so you should get the same autocomplete experience as VS code.
Note that some LSPs are not what I would call lightweight. You might have a lighter experience using Kdevelop's python support, rather than an LSP for example (I've not tested though). Or research to see if alternate LSPs are available for a language.
From what I can tell, raylib is just a library? In which case it should work with any autocomplete (Kdevelop or LSP) for whichever language you use.
Kate includes many default LSP configurations, and links to their download pages in it's LSP settings. LSPs may also be available in your system's package manager.