Refactor search related functionality
This is a prelude to adding the feature of inviting users to
a room, getting everything in the right place and reusable.
What this does:
## User search refactor
Moves the (global) user search logic (dealing with MXIDs,
minimum lengths, debounces) into a `UserRepository`.
This now sits in a `usersearch` library, which will be
used by the create room flow and the new invite flow.
## SearchBar logic pull-up
Every place we use SearchBar, we're doing the same things
to style placeholders, show back/cancel buttons, etc.
We also have a results type that is duplicated for
basically every feature that uses the search bar.
I've pushed all this common functionality into the
SearchBar itself. This makes the component a bit less
general purpose, but saves a lot of repetition.
## Remove the userlist feature
Almost all the functionality of the userlist feature
is now exclusively used by the create room feature.
Room details uses its own version because the
requirements are different.
Components useful elsewhere (SelectedUsers and
SelectedUser) have gone to matrixui, everything else
has gone to createroom.
## Other bits and pieces
I've fixed everywhere that uses Scaffold to correctly
consume the WindowInsets if the contentPadding is
applied to the contents (which it universally is).
This was a change in the last version of Material3
(I guess previously Scaffold handled the consumption
for us). This fixes weird gaps above search bars.
Added overloads for the MatrixUserRow and
CheckedMatrixUserRow that take the name/subtitle/avatar
separately, so the invites list can pass arbitrary
text like "User has already been invited".
The `blockuser` package was for some reason not
under `impl` but alongside it, I've bumped it into
the right place.
