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/api/api.cpp

@@ -29,10 +29,12 @@
 /**************************************************************************/
 
 #include "api.h"
-#include "core/config/engine.h"
+
 #include "javascript_bridge_singleton.h"
 #include "web_tools_editor_plugin.h"
 
+#include "core/config/engine.h"
+
 static JavaScriptBridge *javascript_bridge_singleton;
 
 void register_web_api() {
@@ -78,6 +80,7 @@ void JavaScriptBridge::_bind_methods() {
 }
 
 #if !defined(WEB_ENABLED) || !defined(JAVASCRIPT_EVAL_ENABLED)
+
 Variant JavaScriptBridge::eval(const String &p_code, bool p_use_global_exec_context) {
 	return Variant();
 }
@@ -104,16 +107,23 @@ Variant JavaScriptBridge::_create_object_bind(const Variant **p_args, int p_argc
 	}
 	return Ref<JavaScriptObject>();
 }
+
 #endif
+
 #if !defined(WEB_ENABLED)
+
 bool JavaScriptBridge::pwa_needs_update() const {
 	return false;
 }
+
 Error JavaScriptBridge::pwa_update() {
 	return ERR_UNAVAILABLE;
 }
+
 void JavaScriptBridge::force_fs_sync() {
 }
+
 void JavaScriptBridge::download_buffer(Vector<uint8_t> p_arr, const String &p_name, const String &p_mime) {
 }
+
 #endif