[meson] Put back Experimental-API infrastructure

Just unused for now.

.github/workflows/coverity-scan.yml

@@ -21,7 +21,7 @@ jobs:
           TOKEN: ${{ secrets.COVERITY_SCAN_TOKEN }}
 
       # ideally we should've used meson and ninja here but it complains about coverage or something
-      - run: cov-analysis-linux64/bin/cov-build --dir cov-int clang src/hb-*.cc -DHAVE_FREETYPE -DHAVE_GRAPHITE2 -DHAVE_GLIB -DHAVE_ICU `pkg-config --cflags freetype2 graphite2 glib-2.0 icu-uc` -DHAVE_ROUNDF -DHAVE_SYS_MMAN_H -DHAVE_UNISTD_H -DHAVE_GETPAGESIZE -c
+      - run: cov-analysis-linux64/bin/cov-build --dir cov-int clang src/hb-*.cc -DHAVE_FREETYPE -DHAVE_GRAPHITE2 -DHAVE_GLIB -DHAVE_ICU `pkg-config --cflags freetype2 graphite2 glib-2.0 icu-uc` -DHAVE_ROUNDF -DHAVE_SYS_MMAN_H -DHAVE_UNISTD_H -DHAVE_GETPAGESIZE -DHB_EXPERIMENTAL_API -c
 
       - run: tar czvf harfbuzz.tgz cov-int
 

meson.build

@@ -214,6 +214,10 @@ if get_option('icu_builtin')
   conf.set('HAVE_ICU_BUILTIN', 1)
 endif
 
+if get_option('experimental_api')
+  conf.set('HB_EXPERIMENTAL_API', 1)
+endif
+
 if freetype_dep.found()
   conf.set('HAVE_FREETYPE', 1)
   check_freetype_funcs = [
@@ -394,6 +398,7 @@ build_summary = {
     {'Documentation': conf.get('HAVE_GTK_DOC', 0) == 1,
      'GObject bindings': conf.get('HAVE_GOBJECT', 0) == 1,
      'Introspection': conf.get('HAVE_INTROSPECTION', 0) == 1,
+     'Experimental APIs': conf.get('HB_EXPERIMENTAL_API', 0) == 1,
     },
   'Testing':
     {'Tests': get_option('tests').enabled(),