This is almost one year of changes to EXWM. Note that it undoes our
port of https://github.com/ch11ng/exwm/pull/737
That PR hasn't seen any movement in three years, so it might not be
that relevant anymore. Other stuff has been mainlined in the meantime.
Change-Id: I0845ff8a28a5bb1553855f6d6f0ceeaedcf0809e
A lot has happened in the meantime (EXWM maintainer change) and this
pulls in all the relevant changes since then.
It may become unnecessary to keep EXWM subtreed, but we'll get to that
later.
Change-Id: I45cc06d747d84b3d28fd0db0e4bb3b749a956583