This commit does two things:
* It puts the "minimum supported matrix version" from v1.5 back down to
v1.1. In other words, it is a partial revert of
https://github.com/matrix-org/matrix-js-sdk/pull/3970. (Partial, because we
don't need to update the tests.)
We're doing this largely because
https://github.com/matrix-org/matrix-js-sdk/pull/3970 was introduced without
a suitable announcement and deprecation policy. We haven't yet decided if
the js-sdk's spec support policy needs to change, or if we will re-introduce
this change in future in a more graceful manner.
* It increases the "maximum supported matrix version" from v1.5 up to
v1.9. Previously, the two concepts were tied together, but as discussed at
length in
https://github.com/matrix-org/matrix-js-sdk/issues/3915#issuecomment-1865221366,
this is incorrect.
Unfortunately, we have no real way of testing whether it is true that the
js-sdk actually works with a server which supports *only* v1.9, but as per
the comment above, we can't do much about that.
Fixes https://github.com/matrix-org/matrix-js-sdk/issues/3915.
