N°3526 - Clean up pass on UIBlocks

- Move UIBlock::ENUM_BLOCK_FILES_TYPE_XXX to iUIBlock
- Add PHPDoc
- Remove Object return type hint on overloadable methods
- Add scalar return type hint
- Add type hint on parameters

sources/application/UI/Base/Component/ButtonGroup/ButtonGroup.php

@@ -71,7 +71,7 @@ class ButtonGroup extends UIBlock
 	 * @return \Combodo\iTop\Application\UI\Base\Component\Button\Button[]
 	 * @use static::$aButtons
 	 */
-	public function GetButtons()
+	public function GetButtons(): array
 	{
 		return $this->aButtons;
 	}