Add core extensions: UserCSS, UserJS (#6267)

* Copy CustomCSS and CustomJS

Original: FreshRSS/Extensions@9f21984

* Rename CustomCSS -> UserCSS

* Rename CustomJS -> UserJS

* Change metadata

The name is used for the directory where the configuration
is stored and should not contain spaces.
Since the name was changed, I reset the version number and
changed to semantic versioning.

* Change data directory

Changed the location of the configuration file to
the user data directory, because it is not `static`.
That way, the user's configurations are gathered
in the user directory, which makes it easier to backup them.

* Edit documentations

Remove procedures to install the extension
because it is no longer necessary.

* Fix wrong variables in the configuration page

Remove permission error indication because the storage location
is now in the user data directory managed by the application.

* Remove the `xExtension-` prefix for core extensions

* Set version to 1.0.0 for UserCSS, UserJS

* Refactoring

* Remove unused variables

* Remove version 0.0.1 in Changelog

Version 0.0.1 will not be merged, so only version 1.0.0 will remain.

* public getFileUrl

* Revert more protected

* Use entrypoint for extension user path instead of name

* Add space to extension name

* Add `#[\Override]`

* Add explains of User CSS and User JS to docs

* Remove README of User CSS and User JS

* Add migration code for extension user path

---------

Co-authored-by: Alexandre Alapetite <alexandre@alapetite.fr>

1 files changed, 7 insertions, 2 deletions

diff --git a/docs/en/developers/03_Backend/05_Extensions.md b/docs/en/developers/03_Backend/05_Extensions.md
index 164a309ed..f83d8eef7 100644
--- a/docs/en/developers/03_Backend/05_Extensions.md
+++ b/docs/en/developers/03_Backend/05_Extensions.md
@@ -56,8 +56,11 @@ If you want to write a `HelloWorld` extension, the directory name should be `xEx
 
 In the file `freshrss/extensions/xExtension-HelloWorld/extension.php` you need the structure:
 ```php
-class HelloWorldExtension extends Minz_Extension {
-	public function init() {
+final class HelloWorldExtension extends Minz_Extension {
+	#[\Override]
+	public function init(): void {
+		parent::init();
+
 		// your code here
 	}
 }
@@ -136,6 +139,8 @@ final class HelloWorldExtension extends Minz_Extension
 {
 	#[\Override]
 	public function init(): void {
+		parent::init();
+
 		$this->registerHook('entry_before_display', [$this, 'renderEntry']);
 		$this->registerHook('check_url_before_add', [self::class, 'checkUrl']);
 	}