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/macos/key_mapping_macos.mm

@@ -30,12 +30,12 @@
 
 #include "key_mapping_macos.h"
 
-#import <Carbon/Carbon.h>
-#import <Cocoa/Cocoa.h>
-
 #include "core/templates/hash_map.h"
 #include "core/templates/hash_set.h"
 
+#import <Carbon/Carbon.h>
+#import <Cocoa/Cocoa.h>
+
 struct HashMapHasherKeys {
 	static _FORCE_INLINE_ uint32_t hash(const Key p_key) { return hash_fmix32(static_cast<uint32_t>(p_key)); }
 	static _FORCE_INLINE_ uint32_t hash(const char32_t p_uchar) { return hash_fmix32(p_uchar); }