[base] Add hb_ot_layout_get_baseline API

diff --git a/docs/harfbuzz-sections.txt b/docs/harfbuzz-sections.txt
index 0bc2a2c..f8650b0 100644
--- a/docs/harfbuzz-sections.txt
+++ b/docs/harfbuzz-sections.txt
@@ -548,6 +548,7 @@
 HB_OT_TAG_GPOS
 HB_OT_TAG_GSUB
 HB_OT_TAG_JSTF
+hb_ot_layout_baseline_tag_t
 hb_ot_layout_collect_lookups
 hb_ot_layout_collect_features
 hb_ot_layout_feature_get_characters
@@ -555,6 +556,7 @@
 hb_ot_layout_feature_get_name_ids
 hb_ot_layout_feature_with_variations_get_lookups
 hb_ot_layout_get_attach_points
+hb_ot_layout_get_baseline
 hb_ot_layout_get_glyph_class
 hb_ot_layout_get_glyphs_in_class
 hb_ot_layout_get_ligature_carets