Refactor gUnk9DE568 and gUnk9DE56C to be type of rct_xy16 called gPaintSpritePosition
Rename unk_9ABDA4 to gCurrentColourPalette.
Rename gUnkEDF81C to gCurrentImageType.
Rename sub_679236_679662_679B0D_679FF1 to pixel_is_present.
Remove unused variables _unk9ABDAE, _unk9AC149, unk_9E3CE4, only ever assigned but never read.
Remove unreferenced variable unk_9E3CDC.
Clean up some parts in sub_679236_679662_679B0D_679FF1.
Remove function sub_68371D and references, it assigns variables that are never used.
Add assert determine if unused code.
This commit expands tabs to spaces (ts=4) in all the files under src/
and test/.
Until now we had two wildly different code styles with C using tabs and
new C++ using spaces. It is painful to maintain as none of the commonly
used tools support this kind of setup and in reality is needless, as we
can simply convert all the sources to spaces and have opened PRs do the
same, where needed.
Additionally, trailing whitespace has been removed.
