[android/fs] external content loader + nca/xci patches (#3596)

Foreword: WHY DON'T EVERYBODY USE ONE FOLDER FOR EACH GAME+CONTENTS? AIN'T THIS THE FORMAT GAMES COME WHEN YOU BUE THEM? DO YOU LIVE WITH ALL YOUR FRIENDS AND HAVE A 2ND HOUSE FOR ALL THE CHILDREN?

Nice, i feel better now.

This feat extends Maufeat's work on external content loading. It harmonically additions:
"...also, if in each game folder X, you find a folder Y, and in this folder Y you detect ONLY a single game, then mount all external content for that game found in that folder Y and its subfolders."
Permanent (not toggleable). External Content folders are supported equally.

Also:
-Reworked several routines for preserving single source of truth between android and other systems;
-Fixed the annoying unknown format error for content files, by providing proper format detection.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3596
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Co-authored-by: xbzk <xbzk@eden-emu.dev>
Co-committed-by: xbzk <xbzk@eden-emu.dev>

src/common/settings.h

@@ -756,6 +756,8 @@ struct Values {
                                         Category::DataStorage};
     Setting<std::string> gamecard_path{linkage, std::string(), "gamecard_path",
                                        Category::DataStorage};
+    Setting<bool> ext_content_from_game_dirs{linkage, true, "ext_content_from_game_dirs",
+                                             Category::DataStorage};
     std::vector<std::string> external_content_dirs;
 
     // Debugging