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

src/common/texture.cpp

@@ -3,12 +3,12 @@
 // Refer to the license.txt file included.
 
 #include <algorithm>
-#include <vector>
 #include "common/assert.h"
-#include "common/common_types.h"
+#include "common/texture.h"
 
 namespace Common {
-void FlipRGBA8Texture(std::vector<u8>& tex, u32 width, u32 height) {
+
+void FlipRGBA8Texture(std::span<u8> tex, u32 width, u32 height) {
     ASSERT(tex.size() == width * height * 4);
     const u32 line_size = width * 4;
     for (u32 line = 0; line < height / 2; line++) {
@@ -19,4 +19,5 @@ void FlipRGBA8Texture(std::vector<u8>& tex, u32 width, u32 height) {
                          tex.begin() + offset_2);
     }
 }
+
 } // namespace Common