Replace existing reporting dialogs with reported harms-based flow

This is under "Reporting v2". The new dialog should give the user options to self-categorize their report and optionally provide additional context.

If the https://github.com/matrix-org/matrix-spec-proposals/pull/4457 API is available on the server, the dialog should use that API. If not available, the existing reporting APIs are used instead (with `reason` containing the selected harm identifier alongside the user's other context).

Designs: https://www.figma.com/design/mnYmK2oQzm9mjsATbT8gKG/Reporting?node-id=1-416&p=f&t=UdmfEJ9PoRCI7nHI-0

Ideally both reporting dialogs are unified under this new dialog, and the new dialog is a shared component using MVVM.

(note for maintainers: T&S plans to contribute the vast majority of this, but may need help getting it across the line)