don't show rooms when they're ignored

[jesopo]

based on #8983. will want an additional UI change to warn users that they're looking at an ignored room (with an option to unignore) if they click on a room link for an ignored room

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This PR currently has none of the required changelog labels.

Add one of: T-Deprecation, T-Enhancement, T-Defect, T-Task to indicate what type of change this is plus X-Breaking-Change if it's a breaking change.

[robintown]

Please re-request review from the element-web team when this is no longer a draft

[Yoric]

Upgraded to the latest API (plus applied feedback) in #9255.