shared: add nm_utils_strdict_get_keys() helper

At various places we get the (string) keys of a GHashTable.
Add a helper function that does that, including an argument
for optional sorting.

The helper function is there to get reduce code duplication.

shared/nm-utils/nm-shared-utils.c

@@ -1148,3 +1148,30 @@ nm_utils_named_values_from_str_dict (GHashTable *hash, guint *out_len)
 	NM_SET_OUT (out_len, len);
 	return values;
 }
+
+const char **
+nm_utils_strdict_get_keys (const GHashTable *hash,
+                           gboolean sorted,
+                           guint *out_length)
+{
+	const char **names;
+	guint length;
+
+	if (   !hash
+	    || !g_hash_table_size ((GHashTable *) hash)) {
+		NM_SET_OUT (out_length, 0);
+		return NULL;
+	}
+
+	names = (const char **) g_hash_table_get_keys_as_array ((GHashTable *) hash, &length);
+	if (   sorted
+	    && length > 1) {
+		g_qsort_with_data (names,
+		                   length,
+		                   sizeof (char *),
+		                   nm_strcmp_p_with_data,
+		                   NULL);
+	}
+	NM_SET_OUT (out_length, length);
+	return names;
+}

shared/nm-utils/nm-shared-utils.h

@@ -443,6 +443,10 @@ typedef struct {
 
 NMUtilsNamedValue *nm_utils_named_values_from_str_dict (GHashTable *hash, guint *out_len);
 
+const char **nm_utils_strdict_get_keys (const GHashTable *hash,
+                                        gboolean sorted,
+                                        guint *out_length);
+
 /*****************************************************************************/
 
 #define NM_UTILS_NS_PER_SECOND  ((gint64) 1000000000)