Style: Harmonize header includes in platform ports

This applies our existing style guide, and adds a new rule to that style
guide for modular components such as platform ports and modules:

Includes from the platform port or module should be included with relative
paths (relative to the root folder of the modular component, e.g.
`platform/linuxbsd/`), in their own section before Godot's "core" includes.

The `api` and `export` subfolders also need to be handled as self-contained
(and thus use relative paths for their "local" includes) as they are all
compiled for each editor platform, without necessarily having the api/export
matching platform folder in the include path.
E.g. the Linux editor build will compile `platform/android/{api,export}/*.cpp`
and those need to use relative includes for it to work.

platform/web/audio_driver_web.h

@@ -31,12 +31,12 @@
 #ifndef AUDIO_DRIVER_WEB_H
 #define AUDIO_DRIVER_WEB_H
 
+#include "godot_audio.h"
+
 #include "core/os/mutex.h"
 #include "core/os/thread.h"
 #include "servers/audio_server.h"
 
-#include "godot_audio.h"
-
 class AudioDriverWeb : public AudioDriver {
 private:
 	struct AudioContext {