id128-util: add new helper id128_equal_string()

Quite often we compare uuids/id128 formatted as strings with specific
values. So far we usually used streq() for that. let's add a new
explicit helper for this in id128_equal_string() that compares a string
with an sd_id128_t and is more robust than a simple string comparison.
Moreover, we can mroe easily reuse the various defines we have for
specific UUIDs, for example those from gpt.h.

src/libsystemd/sd-id128/id128-util.c

@@ -206,3 +206,19 @@ int id128_get_product(sd_id128_t *ret) {
         *ret = uuid;
         return 0;
 }
+
+int id128_equal_string(const char *s, sd_id128_t id) {
+        sd_id128_t parsed;
+        int r;
+
+        if (!s)
+                return false;
+
+        /* Checks if the specified string matches a valid string representation of the specified 128 bit ID/uuid */
+
+        r = sd_id128_from_string(s, &parsed);
+        if (r < 0)
+                return r;
+
+        return sd_id128_equal(parsed, id);
+}

src/libsystemd/sd-id128/id128-util.h

@@ -34,3 +34,5 @@ extern const struct hash_ops id128_hash_ops;
 sd_id128_t id128_make_v4_uuid(sd_id128_t id);
 
 int id128_get_product(sd_id128_t *ret);
+
+int id128_equal_string(const char *s, sd_id128_t id);