spa: utils: string: introduce spa_str_find()

spa_str_find() may be used to check whether a string
exists in an array of strings (subject to an arbitrary three-way comparator)
and optinally retrieve its index.

spa/include/spa/utils/string.h

@@ -291,6 +291,40 @@ static inline bool spa_atod(const char *str, double *val)
 	return true;
 }
 
+/**
+ * Find \a needle in the \a haystack array of \a n strings.
+ *
+ * \param haystack an array of \a n strings
+ * \param n number of strings in \a haystack
+ * \param cmp a three-way comparator
+ * \param index pointer to save the index into if \a needle is found,
+ *        may be NULL; it is not modified if \a needle is not found
+ *
+ * \return true if \a needle is found, false otherwise
+ *
+ * \since 0.3.31
+ */
+static inline bool spa_find_str(const char * const haystack[], size_t n,
+				const char *needle,
+				int (*cmp)(const char *, const char *),
+				size_t *index)
+{
+	for (size_t i = 0; i < n; i++) {
+		if (cmp(needle, haystack[i]) != 0)
+			continue;
+
+		if (index != NULL)
+			*index = i;
+
+		return true;
+	}
+
+	return false;
+}
+
+#define spa_find_str_arr(haystack, needle, cmp, index) \
+	(spa_find_str((haystack), SPA_N_ELEMENTS(haystack), (needle), (cmp), (index)))
+
 /**
  * \}
  */