[sfnt] Load variation store for 'COLR' v1.

* src/sfnt/ttcolr.c: Include `ttobjs.h` temporarily.
(VARIABLE_COLRV1_ENABLED): New temporary macro to detect whether variable
COLRv1 is enabled.
(Colr): New fields `var_store` and `delta_set_idx_map`.
(tt_face_load_colr, tt_face_free_colr) [VARIABLE_COLRV1_ENABLED]: Load and
free variation store data using the functions from the Multiple Masters
service.
13 jobs for master in 13 minutes and 45 seconds (queued for 2 seconds)