Simplify foliage rendering

[glebm]

During ReencodeDungeonCels, extracts floor tile foliage into a triangle with the floor frame and a separate 16-px tall TransparentSquare.

This means that the floor frames are now always triangles and the foliage can be rendered directly without masking.

Dungeon graphics sizes:

Map	Frames	Foliage frames	Byte size	Before PR	After PR
Town	3,803	41	2,317,832	2,242,056	2,242,190
L1	1,119	11	738,836	721,604	721,110
L4	1,091	6	603,140	584,500	584,242

RG99 binary size reduced by ~4 KiB: 2,426,380 bytes -> 2,421,388 bytes

[AJenbo]

uh, this has a conflict now :o

[glebm]

Rebased

[AJenbo]

Nice to have it split the data like this, also good to have the comments to explain what it's doing.