Add link property to MXKRoomBubbleComponent and parse events for links.

[pixlwave]

As part of https://github.com/vector-im/element-ios/pull/4790, the change to MatrixKit for URL previews include the following:

• A link property on MXKRoomBubbleComponent.
• Link detection on creation and update of MXKRoomBubbleComponent.
• Links are only detected for unencrypted message events.
• Link detection is controlled by an MXKAppSettings which is disabled by default (but enabled in the Element PR).
• Fixes a crash that could occur reloading the timeline data whilst also rotating the device.