GDExtension: Implement GDExtensionLoader concept

- Implements the concept of GDExtension loaders that can be used to customize how GDExtensions are loaded and initialized.
- Moves the parsing of `.gdextension` config files to the new `GDExtensionLibraryLoader`.
- `GDExtensionManager` is now meant to be the main way to load/unload extensions and can optionally take a `GDExtensionLoader`.
- `EditorFileSystem` avoids unloading extensions if the file still exists, this should prevent unloading extensions that are outside the user project.

core/extension/gdextension.h

@@ -31,13 +31,11 @@
 #ifndef GDEXTENSION_H
 #define GDEXTENSION_H
 
-#include <functional>
-
 #include "core/extension/gdextension_interface.h"
+#include "core/extension/gdextension_loader.h"
 #include "core/io/config_file.h"
 #include "core/io/resource_loader.h"
 #include "core/object/ref_counted.h"
-#include "core/os/shared_object.h"
 
 class GDExtensionMethodBind;
 
@@ -46,8 +44,8 @@ class GDExtension : public Resource {
 
 	friend class GDExtensionManager;
 
-	void *library = nullptr; // pointer if valid,
-	String library_path;
+	Ref<GDExtensionLoader> loader;
+
 	bool reloadable = false;
 
 	struct Extension {
@@ -96,8 +94,6 @@ class GDExtension : public Resource {
 	int32_t level_initialized = -1;
 
 #ifdef TOOLS_ENABLED
-	uint64_t resource_last_modified_time = 0;
-	uint64_t library_last_modified_time = 0;
 	bool is_reloading = false;
 	Vector<GDExtensionMethodBind *> invalid_methods;
 	Vector<ObjectID> instance_bindings;
@@ -124,11 +120,12 @@ class GDExtension : public Resource {
 	virtual bool editor_can_reload_from_file() override { return false; } // Reloading is handled in a special way.
 
 	static String get_extension_list_config_file();
-	static String find_extension_library(const String &p_path, Ref<ConfigFile> p_config, std::function<bool(String)> p_has_feature, PackedStringArray *r_tags = nullptr);
-	static Vector<SharedObject> find_extension_dependencies(const String &p_path, Ref<ConfigFile> p_config, std::function<bool(String)> p_has_feature);
 
-	Error open_library(const String &p_path, const String &p_entry_symbol, Vector<SharedObject> *p_dependencies = nullptr);
+	const Ref<GDExtensionLoader> get_loader() const { return loader; }
+
+	Error open_library(const String &p_path, const Ref<GDExtensionLoader> &p_loader);
 	void close_library();
+	bool is_library_open() const;
 
 	enum InitializationLevel {
 		INITIALIZATION_LEVEL_CORE = GDEXTENSION_INITIALIZATION_CORE,
@@ -146,17 +143,11 @@ class GDExtension : public Resource {
 #endif
 
 public:
-	bool is_library_open() const;
-
 #ifdef TOOLS_ENABLED
 	bool is_reloadable() const { return reloadable; }
 	void set_reloadable(bool p_reloadable) { reloadable = p_reloadable; }
 
 	bool has_library_changed() const;
-	void update_last_modified_time(uint64_t p_resource_last_modified_time, uint64_t p_library_last_modified_time) {
-		resource_last_modified_time = p_resource_last_modified_time;
-		library_last_modified_time = p_library_last_modified_time;
-	}
 
 	void track_instance_binding(Object *p_object);
 	void untrack_instance_binding(Object *p_object);