Rework new lines around list BBCode

- Remove blanket new lines remover in HTML::toBBCode
- Add test to ensure the commutativity of the markups

tests/src/Content/Text/BBCodeTest.php

@@ -265,7 +265,15 @@ Karl Marx - Die ursprüngliche Akkumulation
 			'task-12900-header-with-paragraphs' => [
 				'expectedHTML' => '<h1>Header</h1><p>Some Chapter</p>',
 				'text' => '[h1]Header[/h1]Some Chapter',
-			]
+			],
+			'bug-12842-ul-newlines' => [
+				'expectedHTML' => '<p>This is:</p><ul><li>some<br></li><li>amazing<br></li><li>list</li></ul>',
+				'text' => "This is:\r\n[ul]\r\n[*]some\r\n[*]amazing\r\n[*]list\r\n[/ul]",
+			],
+			'bug-12842-ol-newlines' => [
+				'expectedHTML' => '<p>This is:</p><ol><li>some<br></li><li>amazing<br></li><li>list</li></ol>',
+				'text' => "This is:\r\n[ol]\r\n[*]some\r\n[*]amazing\r\n[*]list\r\n[/ol]",
+			],
 		];
 	}