Move modifier name table to common/util.c

Lookup of modifier names is required in several places, thus it makes
sense to move it to a general place.

include/util.h

@@ -1,6 +1,10 @@
 #ifndef _SWAY_UTIL_H
 #define _SWAY_UTIL_H
 
+#include <stdint.h>
+#include <wlc/wlc.h>
+#include <xkbcommon/xkbcommon.h>
+
 /**
  * Wrap i into the range [0, max[
  */
@@ -11,4 +15,18 @@ int wrap(int i, int max);
  */
 int numlen(int n);
 
+/**
+ * Get modifier mask from modifier name.
+ *
+ * Returns the modifer mask or 0 if the name isn't found.
+ */
+uint32_t get_modifier_mask_by_name(const char *name);
+
+/**
+ * Get modifier name from modifier mask.
+ *
+ * Returns the modifier name or NULL if it isn't found.
+ */
+const char *get_modifier_name_by_mask(uint32_t modifier);
+
 #endif