composetable: Parse hex escapes too

This was a small omission from the Compose file
syntax that doesn't cost us much to support.

Add a test for this syntax too.

Fixes: #1004

gtk/gtkcomposetable.c

@@ -113,6 +113,22 @@ parse_compose_value (GtkComposeData *compose_data,
           else if (p[1] >= '0' && p[1] < '8')
             {
               ch = g_ascii_strtoll (p + 1, &endp, 8);
+              if (ch == 0)
+                {
+                  g_warning ("Invalid escape sequence: %s: %s", val, line);
+                  goto fail;
+                }
+              g_string_append_unichar (value, ch);
+              p = endp;
+            }
+          else if (p[1] == 'x' || p[1] == 'X')
+            {
+              ch = g_ascii_strtoll (p + 2, &endp, 16);
+              if (ch == 0)
+                {
+                  g_warning ("Invalid escape sequence: %s: %s", val, line);
+                  goto fail;
+                }
               g_string_append_unichar (value, ch);
               p = endp;
             }

testsuite/gtk/compose/hex

@@ -0,0 +1 @@
+<Multi_key> <s> <e> <q> : "\x23fe\X23F3"

testsuite/gtk/compose/hex.expected

@@ -0,0 +1,3 @@
+# n_seqs: 1
+# max_seq_len: 4
+<Uff20> <U73> <U65> <U71> : "⏾⏳"

testsuite/gtk/composetable.c

@@ -308,6 +308,7 @@ main (int argc, char *argv[])
   g_test_add_data_func ("/compose-table/basic", "basic", compose_table_compare);
   g_test_add_data_func ("/compose-table/long", "long", compose_table_compare);
   g_test_add_data_func ("/compose-table/octal", "octal", compose_table_compare);
+  g_test_add_data_func ("/compose-table/hex", "hex", compose_table_compare);
   g_test_add_data_func ("/compose-table/codepoint", "codepoint", compose_table_compare);
   g_test_add_data_func ("/compose-table/multi", "multi", compose_table_compare);
   g_test_add_data_func ("/compose-table/strings", "strings", compose_table_compare);