Require that server copy the room type when upgrading rooms

[Mikaela]

Suggestion

If I understand correctly, Element Web doesn't allow upgrading spaces as there is no mechanism for them to know that the homeserver will perform the operation correctly (without losing the information that the room is a space).

• Allow upgrading Spaces element-hq/element-meta#1961

[Mikaela]

It looks like this may get resolved by matrix-org/matrix-spec-proposals#3385 and I think this also prevents upgrading matrix-org/matrix-spec-proposals#3588 rooms (or at least I am yet to get told otherwise in a week)

[clokep]

Note that Synapse actually does this already for spaces: matrix-org/synapse#10774

[turt2live]

ftr, the spec currently makes it an implementation detail for the field to carry over - open to suggestions (meaning MSCs) which discuss a different approach.