build: lint header files with clang-tidy (#7527)

* build: clang-tidy headers when building libtransmission

* chore: revert `= default` workaround

It was introduced in 6909ec0bad to fix build issues with macOS 10.14. We
no longer support that version.

* fix: clang-tidy warnings for libtransmission

* build: clang-tidy headers when building tests

* fix: clang-tidy warnings for tests

* build: clang-tidy headers when building qt

* code review: don't manually edit mime-types.h

* code review: unify variable naming for static private members

libtransmission/quark.h

@@ -19,7 +19,7 @@ using tr_quark = size_t;
  * between RPC and settings. This will be a mess and we shouldn't be
  * in a hurry to do it.
  */
-enum
+enum // NOLINT(performance-enum-size)
 {
     TR_KEY_NONE, /* represented as an empty string */
     TR_KEY_activeTorrentCount, /* rpc */