Implement shader caching

* Shader compilation is now cached. Subsequent loads take less than a millisecond.
* Improved game, editor and project manager startup time.
* Editor uses .godot/shader_cache to store shaders.
* Game uses user://shader_cache
* Project manager uses $config_dir/shader_cache
* Options to tweak shader caching in project settings.
* Editor path configuration moved from EditorSettings to new class, EditorPaths, so it can be available early on (before shaders are compiled).
* Reworked ShaderCompilerRD to ensure deterministic shader code creation (else shader may change and cache will be invalidated).
* Added shader compression with SMOLV: https://github.com/aras-p/smol-v

core/config/engine.cpp

@@ -31,6 +31,7 @@
 #include "engine.h"
 
 #include "core/authors.gen.h"
+#include "core/config/project_settings.h"
 #include "core/donors.gen.h"
 #include "core/license.gen.h"
 #include "core/version.h"
@@ -210,6 +211,13 @@ void Engine::get_singletons(List<Singleton> *p_singletons) {
 	}
 }
 
+void Engine::set_shader_cache_path(const String &p_path) {
+	shader_cache_path = p_path;
+}
+String Engine::get_shader_cache_path() const {
+	return shader_cache_path;
+}
+
 Engine *Engine::singleton = nullptr;
 
 Engine *Engine::get_singleton() {