Split VoiceOver accessibility into 4 logical patches:
0001: Base classes + text extraction (+753)
0002: Buffer/ModeLine/InteractiveSpan implementations (+1716)
0003: EmacsView integration + cursor tracking (+395)
0004: Documentation with known limitations (+75)
Each patch is self-contained: 0001 adds infrastructure that compiles
but doesn't change behavior. 0002 adds protocol implementations.
0003 wires everything into EmacsView. 0004 documents for users.
All patches verified: apply cleanly to current Emacs master,
final state identical to original monolithic patch.
