Custom textures rewrite (#6452)

* common: Add thread pool from yuzu

* Is really useful for asynchronous operations like shader compilation and custom textures, will be used in following PRs

* core: Improve ImageInterface

* Provide a default implementation so frontends don't have to duplicate code registering the lodepng version

* Add a dds version too which we will use in the next commit

* rasterizer_cache: Rewrite custom textures

* There's just too much to talk about here, look at the PR description for more details

* rasterizer_cache: Implement basic pack configuration file

* custom_tex_manager: Flip dumped textures

* custom_tex_manager: Optimize custom texture hashing

* If no convertions are needed then we can hash the decoded data directly removing the needed for duplicate decode

* custom_tex_manager: Implement asynchronous texture loading

* The file loading and decoding is offloaded into worker threads, while the upload itself still occurs in the main thread to avoid having to manage shared contexts

* Address review comments

* custom_tex_manager: Introduce custom material support

* video_core: Move custom textures to separate directory

* Also split the files to make the code cleaner

* gl_texture_runtime: Generate mipmaps for material

* custom_tex_manager: Prevent memory overflow when preloading

* externals: Add dds-ktx as submodule

* string_util: Return vector from SplitString

* No code benefits from passing it as an argument

* custom_textures: Use json config file

* gl_rasterizer: Only bind material for unit 0

* Address review comments

externals/CMakeLists.txt

@@ -64,6 +64,10 @@ if(ANDROID)
     endforeach()
 endif()
 
+# dds-ktx
+add_library(dds-ktx INTERFACE)
+target_include_directories(dds-ktx INTERFACE ./dds-ktx)
+
 # fmt and Xbyak need to be added before dynarmic
 # libfmt
 option(FMT_INSTALL "" ON)
@@ -141,6 +145,10 @@ if (USE_DISCORD_PRESENCE)
     target_include_directories(discord-rpc INTERFACE ./discord-rpc/include)
 endif()
 
+# JSON
+add_library(json-headers INTERFACE)
+target_include_directories(json-headers INTERFACE ./json)
+
 if (ENABLE_WEB_SERVICE)
     find_package(OpenSSL 1.1)
     if (OPENSSL_FOUND)
@@ -156,9 +164,6 @@ if (ENABLE_WEB_SERVICE)
             DIRECTORY libressl
             DEFINITION OPENSSL_LIBS)
     endif()
-    # JSON
-    add_library(json-headers INTERFACE)
-    target_include_directories(json-headers INTERFACE ./json)
 
     if(ANDROID)
         add_subdirectory(android-ifaddrs)