enhance preprocessor block folding so each if/ifdef/elseif/else block can fold separately

[Traben-0]

Description

preprocessor comment blocks can now fold each if/ifdef/elseif/else block separately, rather than the entire block from #if -> #endif

specifically #if now not only folds to #endif but also to the end of the line before any #else or #elseif which then starts a new fold from the #else or #elseif, which behaves the same way

this makes folding far more usable with nested/complex preprocessor comment blocks, and also sets things up for a possible "collapse inactive blocks by default" option which i want to try add eventually

How to test

vid example \/

Recording.2025-09-27.065402.mp4

Release Notes

- preprocessor comment blocks can now fold each if/ifdef/elseif/else block separately, rather than the entire block from #if -> #endif

[Traben-0]

note this implementation doesn't track the ordering of the else and elseif blocks, and folds them in any order.

but the warning highlight about that remains visible when folded so i dont think thats a concern here