Ensure riot is room v3 ready

[turt2live]

• Verify URLs use encoded event IDs: Escape eventIds in CS API requests riot-meta#261
• Fix Room v3 permalinks don't always work #8315

[turt2live]

part 1/2 is done here, so closing in favour of #8315 to track it

No real point in having such a small todo list as a dedicated thing.