This should alleviate https://github.com/vector-im/element-web/issues/15705 from happening, though the cause is still unknown.
Requiring a room ID is safe for this because only room widgets can be pinned, and widget IDs are not globally unique which means from a logical standpoint the contract still makes sense here.
Following https://github.com/matrix-org/matrix-react-sdk/pull/5385, it is now possible for a widget to request these capabilities without being a video conference or sticker picker. This commit actually enables this support for those kinds of widgets.
This commit also fixes an issue in the URL templating where some variables might get set to 'undefined' - this appears to be a scoping issue, so StopGapWidget now stores the definition alongside the superclass.
Fixes https://github.com/vector-im/element-web/issues/15001
