[aat] Tweak fallback positioning logic when applying morx Such that for Indic-like scripts (eg. Khmer), we don't do any fallback mark advance-zeroing / positioning, but we do for Latin, etc. Reuses preferences of our script-specific OpenType shapers for those. Fixes regression: https://github.com/harfbuzz/harfbuzz/issues/1393 Which means, fixes again: https://github.com/harfbuzz/harfbuzz/issues/1264 While not regressing: https://github.com/harfbuzz/harfbuzz/issues/1357