Expose OS data directory getter methods

This can be used by editor plugins and non-game applications to
store data in the correct directories according to the
XDG Base Directory specification.

core/core_bind.cpp

@@ -426,6 +426,21 @@ String _OS::get_external_data_dir() const {
 	return OS::get_singleton()->get_external_data_dir();
 }
 
+String _OS::get_config_dir() const {
+	// Exposed as `get_config_dir()` instead of `get_config_path()` for consistency with other exposed OS methods.
+	return OS::get_singleton()->get_config_path();
+}
+
+String _OS::get_data_dir() const {
+	// Exposed as `get_data_dir()` instead of `get_data_path()` for consistency with other exposed OS methods.
+	return OS::get_singleton()->get_data_path();
+}
+
+String _OS::get_cache_dir() const {
+	// Exposed as `get_cache_dir()` instead of `get_cache_path()` for consistency with other exposed OS methods.
+	return OS::get_singleton()->get_cache_path();
+}
+
 bool _OS::is_debug_build() const {
 #ifdef DEBUG_ENABLED
 	return true;
@@ -518,6 +533,9 @@ void _OS::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_user_data_dir"), &_OS::get_user_data_dir);
 	ClassDB::bind_method(D_METHOD("get_external_data_dir"), &_OS::get_external_data_dir);
 	ClassDB::bind_method(D_METHOD("get_system_dir", "dir"), &_OS::get_system_dir);
+	ClassDB::bind_method(D_METHOD("get_config_dir"), &_OS::get_config_dir);
+	ClassDB::bind_method(D_METHOD("get_data_dir"), &_OS::get_data_dir);
+	ClassDB::bind_method(D_METHOD("get_cache_dir"), &_OS::get_cache_dir);
 	ClassDB::bind_method(D_METHOD("get_unique_id"), &_OS::get_unique_id);
 
 	ClassDB::bind_method(D_METHOD("print_all_textures_by_size"), &_OS::print_all_textures_by_size);

core/core_bind.h

@@ -230,6 +230,9 @@ public:
 
 	String get_user_data_dir() const;
 	String get_external_data_dir() const;
+	String get_config_dir() const;
+	String get_data_dir() const;
+	String get_cache_dir() const;
 
 	Error set_thread_name(const String &p_name);
 	Thread::ID get_thread_caller_id() const;

doc/classes/OS.xml

@@ -136,6 +136,14 @@
 				Returns the keycode of the given string (e.g. "Escape").
 			</description>
 		</method>
+		<method name="get_cache_dir" qualifiers="const">
+			<return type="String">
+			</return>
+			<description>
+				Returns the [i]global[/i] cache data directory according to the operating system's standards. On desktop platforms, this path can be overridden by setting the [code]XDG_CACHE_HOME[/code] environment variable before starting the project. See [url=https://docs.godotengine.org/en/latest/tutorials/io/data_paths.html]File paths in Godot projects[/url] in the documentation for more information. See also [method get_config_dir] and [method get_data_dir].
+				Not to be confused with [method get_user_data_dir], which returns the [i]project-specific[/i] user data path.
+			</description>
+		</method>
 		<method name="get_cmdline_args">
 			<return type="PackedStringArray">
 			</return>
@@ -167,6 +175,14 @@
 				[/codeblocks]
 			</description>
 		</method>
+		<method name="get_config_dir" qualifiers="const">
+			<return type="String">
+			</return>
+			<description>
+				Returns the [i]global[/i] user configuration directory according to the operating system's standards. On desktop platforms, this path can be overridden by setting the [code]XDG_CONFIG_HOME[/code] environment variable before starting the project. See [url=https://docs.godotengine.org/en/latest/tutorials/io/data_paths.html]File paths in Godot projects[/url] in the documentation for more information. See also [method get_cache_dir] and [method get_data_dir].
+				Not to be confused with [method get_user_data_dir], which returns the [i]project-specific[/i] user data path.
+			</description>
+		</method>
 		<method name="get_connected_midi_inputs">
 			<return type="PackedStringArray">
 			</return>
@@ -176,6 +192,14 @@
 				[b]Note:[/b] This method is implemented on Linux, macOS and Windows.
 			</description>
 		</method>
+		<method name="get_data_dir" qualifiers="const">
+			<return type="String">
+			</return>
+			<description>
+				Returns the [i]global[/i] user data directory according to the operating system's standards. On desktop platforms, this path can be overridden by setting the [code]XDG_DATA_HOME[/code] environment variable before starting the project. See [url=https://docs.godotengine.org/en/latest/tutorials/io/data_paths.html]File paths in Godot projects[/url] in the documentation for more information. See also [method get_cache_dir] and [method get_config_dir].
+				Not to be confused with [method get_user_data_dir], which returns the [i]project-specific[/i] user data path.
+			</description>
+		</method>
 		<method name="get_environment" qualifiers="const">
 			<return type="String">
 			</return>
@@ -310,6 +334,7 @@
 				On macOS, this is [code]~/Library/Application Support/Godot/app_userdata/[project_name][/code], or [code]~/Library/Application Support/[custom_name][/code] if [code]use_custom_user_dir[/code] is set.
 				On Windows, this is [code]%APPDATA%\Godot\app_userdata\[project_name][/code], or [code]%APPDATA%\[custom_name][/code] if [code]use_custom_user_dir[/code] is set. [code]%APPDATA%[/code] expands to [code]%USERPROFILE%\AppData\Roaming[/code].
 				If the project name is empty, [code]user://[/code] falls back to [code]res://[/code].
+				Not to be confused with [method get_data_dir], which returns the [i]global[/i] (non-project-specific) user data directory.
 			</description>
 		</method>
 		<method name="has_environment" qualifiers="const">