Style: Partially apply clang-tidy's cppcoreguidelines-pro-type-member-init

Didn't commit all the changes where it wants to initialize a struct
with `{}`. Should be reviewed in a separate PR.

Option `IgnoreArrays` enabled for now to be conservative, can be
disabled to see if it proposes more useful changes.

Also fixed manually a handful of other missing initializations / moved
some from constructors.

editor/fileserver/editor_file_server.cpp

@@ -311,9 +311,6 @@ void EditorFileServer::stop() {
 
 EditorFileServer::EditorFileServer() {
 	server.instantiate();
-	quit = false;
-	active = false;
-	cmd = CMD_NONE;
 	thread.start(_thread_start, this);
 
 	EDITOR_DEF("filesystem/file_server/port", 6010);