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/thread_worker.h

@@ -0,0 +1,123 @@
+// Copyright 2020 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <atomic>
+#include <condition_variable>
+#include <functional>
+#include <mutex>
+#include <string>
+#include <thread>
+#include <type_traits>
+#include <vector>
+#include <queue>
+
+#include "common/polyfill_thread.h"
+#include "common/thread.h"
+#include "common/unique_function.h"
+
+namespace Common {
+
+template <class StateType = void>
+class StatefulThreadWorker {
+    static constexpr bool with_state = !std::is_same_v<StateType, void>;
+
+    struct DummyCallable {
+        int operator()(size_t) const noexcept {
+            return 0;
+        }
+    };
+
+    using Task =
+        std::conditional_t<with_state, UniqueFunction<void, StateType*>, UniqueFunction<void>>;
+    using StateMaker =
+        std::conditional_t<with_state, std::function<StateType(size_t)>, DummyCallable>;
+
+public:
+    explicit StatefulThreadWorker(size_t num_workers, std::string_view name, StateMaker func = {})
+        : workers_queued{num_workers}, thread_name{name} {
+        const auto lambda = [this, func](std::stop_token stop_token, size_t index) {
+            Common::SetCurrentThreadName(thread_name.data());
+            {
+                [[maybe_unused]] std::conditional_t<with_state, StateType, int> state{func(index)};
+                while (!stop_token.stop_requested()) {
+                    Task task;
+                    {
+                        std::unique_lock lock{queue_mutex};
+                        if (requests.empty()) {
+                            wait_condition.notify_all();
+                        }
+                        Common::CondvarWait(condition, lock, stop_token,
+                                            [this] { return !requests.empty(); });
+                        if (stop_token.stop_requested()) {
+                            break;
+                        }
+                        task = std::move(requests.front());
+                        requests.pop();
+                    }
+                    if constexpr (with_state) {
+                        task(&state);
+                    } else {
+                        task();
+                    }
+                    ++work_done;
+                }
+            }
+            ++workers_stopped;
+            wait_condition.notify_all();
+        };
+        threads.reserve(num_workers);
+        for (size_t i = 0; i < num_workers; ++i) {
+            threads.emplace_back(lambda, i);
+        }
+    }
+
+    StatefulThreadWorker& operator=(const StatefulThreadWorker&) = delete;
+    StatefulThreadWorker(const StatefulThreadWorker&) = delete;
+
+    StatefulThreadWorker& operator=(StatefulThreadWorker&&) = delete;
+    StatefulThreadWorker(StatefulThreadWorker&&) = delete;
+
+    void QueueWork(Task work) {
+        {
+            std::unique_lock lock{queue_mutex};
+            requests.emplace(std::move(work));
+            ++work_scheduled;
+        }
+        condition.notify_one();
+    }
+
+    void WaitForRequests(std::stop_token stop_token = {}) {
+        std::stop_callback callback(stop_token, [this] {
+            for (auto& thread : threads) {
+                thread.request_stop();
+            }
+        });
+        std::unique_lock lock{queue_mutex};
+        wait_condition.wait(lock, [this] {
+            return workers_stopped >= workers_queued || work_done >= work_scheduled;
+        });
+    }
+
+    const std::size_t NumWorkers() const noexcept {
+        return threads.size();
+    }
+
+private:
+    std::queue<Task> requests;
+    std::mutex queue_mutex;
+    std::condition_variable_any condition;
+    std::condition_variable wait_condition;
+    std::atomic<size_t> work_scheduled{};
+    std::atomic<size_t> work_done{};
+    std::atomic<size_t> workers_stopped{};
+    std::atomic<size_t> workers_queued{};
+    std::string_view thread_name;
+    std::vector<std::jthread> threads;
+};
+
+using ThreadWorker = StatefulThreadWorker<>;
+
+} // namespace Common