[woff2] Handle TTCs and start reconstructing font. We `handle' TTCs by modifying the `indices' array to point to only those tables that are part of the requested `face_index'. Set and use `num_tables' in `WOFF2_TtcFont'. * src/sfnt/sfwoff2.c (reconstruct_font): New function. (woff2_open_font): Start reconstruction of font.