This should simplify how some of the code reads, as well as allowing for future
feature additions to be accomplished in a less restrictive manner. The slotmap +
Object enum pattern was kind of like a really bad ecs in a way anyway. Also I
was looking for an excuse to use an ecs.
The -displayfd argument is much friendlier to testing and is generally
more stable. As a result, omitting the display argument to the program
will result in Xwayland searching for the next available display. This
also allows integration tests to run simultaneously and when there is
already an X server running on the system.
This commit also changes how the state of the program is communicated
with integration tests (via the RunData trait).
