modernization: tweaks for c++20

Update various places for what we can do with C++20:

- ends_with / starts_with
- std::to_array
- using instead of typedef
- designated initializers
- "[[maybe_unused]]" instead of G_GNUC_UNUSED

Also remove some unnecessary 'static'

lib/utils/mu-unbroken.hh

@@ -37,7 +37,7 @@
  *
  * @return true or false
  */
-static inline bool
+inline bool
 is_unbroken_script(unsigned p)
 {
 	// Array containing the last value in each range of codepoints which