[util] Add quiet mode to hb-subset-depend

Add -q/--quiet to build and validate a dependency graph without spending
time formatting or printing it. This makes graph-construction profiling
and performance measurements straightforward.

Tested with the full Meson test suite (270/270 passed).

Assisted-by: OpenAI Codex <codex@openai.com>

util/hb-subset-depend.cc

diff --git a/util/hb-subset-depend.cc b/util/hb-subset-depend.cc
index d58fca9..b922ebf 100644
--- a/util/hb-subset-depend.cc
+++ b/util/hb-subset-depend.cc
@@ -38,6 +38,7 @@
   gboolean flagged_only = false;
   gboolean no_context = false;
   gboolean no_glyph_names = false;
+  gboolean quiet = false;
   char *gids_str = nullptr;
 
   void
@@ -60,6 +61,8 @@
        "Suppress context set output", nullptr},
       {"no-glyph-names", 0, 0, G_OPTION_ARG_NONE, &this->no_glyph_names,
        "Use numeric glyph IDs instead of names", nullptr},
+      {"quiet",          'q', 0, G_OPTION_ARG_NONE, &this->quiet,
+       "Build the dependency graph without printing it", nullptr},
       {nullptr}
     };
     add_group (depend_entries,
@@ -209,6 +212,12 @@
       return 1;
     }
 
+    if (quiet)
+    {
+      hb_subset_depend_destroy (depend);
+      return 0;
+    }
+
     hb_font_t *font = no_glyph_names ? nullptr : hb_font_create (face);
 
     std::set<unsigned> gid_filter;