[Tracking Issue] Planned MSC support

[MTRNord]

This issue lists MSCs planned to be added or at least considered.

• MSC3575: Sliding Sync (aka Sync v3) - If I am going to build a new SDK from scratch, I might as well use this directly. Also, this seems to fit the redux world better.
• MSC3767: Time based notification filtering - For worktime notification presets
• MSC3088: Room subtyping - For marking rooms as microblogging, allowing for extended richtext editor features (Not needed anymore)
• MSC3964: Notifications for room tags - Just seems like a sane thing to implement while I am at it anyway
• Explicitly opt out of implementing OIDC due to the core issues of the MSCs which seem to be actively ignored
• Widgets (even considering how bad the spec on it is. aka there being no spec essentially)
• ...