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/Html/Html.php

@@ -55,7 +55,7 @@ class Html extends UIBlock
 	 *
 	 * @return string
 	 */
-	public function GetHtml()
+	public function GetHtml(): string
 	{
 		return $this->sHtml;
 	}