Set `history_visibility` to `invited` for a new DM and room that is not `public`.

[mxandreas]

In short, the requested change is:

• When the user creates a DM, the history_visibility should be set to invited.
• When the user creates a room which is NOT public (join rule is NOT public), the history_visibility should be set to invited.

In both cases it is currently set to shared which has confirmed to be a mistake in the past or at least something that is no longer reasonable. It does not make any sense for DM, and although it may not be a problem in most cases (as you do not invite into a DM most of the time), it is still weird to see that history is shared with new members.

Similarly, for non-public rooms, our current best option is to go with the invited by default, as this is the safest option. Some use cases require indeed shared but it is safer if the user then changes it, than another user discovers that their history has been shared while they did not want that. In the future, it will also enable us to stop allowing changes to history sharing in the direction shared > invited as it is not comprehensible for the users.

Full background and discussion in element-hq/element-meta#3109