Previously it transformed a physical CRTC coordinate to a logical desktop
coordinate. But current and future users of the function all require
conversion from logical coordinates to physical coordinates. We would have
had to always invert the transform parameter which is a waste of time when
we can instead just invert the function behaviour.
We also simplify the parameters to show both the point coordinate and the
area dimensions are potentially transformed.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3180>
The following implicit definition for `transform()` did not
correctly apply:
```
a * b = c
c * invert(b) = a
```
Crucially the following did not apply for `FLIPPED-90`
and `FLIPPED-270`:
```
a * invert(a) = identity
```
Fix this by applying the operations, first the flip, then the
rotation, in this order and add tests to ensure correct results
for the requirement above.
Also drop `relative_transform()` as it only had a single user and
can be replaced by `transform()`:
```
invert(a) * b = c
a * c = b
```
As this is not very intuitive, ensure in tests as well.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2459>
Commit 25f416c13d added additional compilation warnings, including
-Werror=return-type. There are several places where this results
in build failures if `g_assert_not_reached()` is disabled at compile
time and the compiler misses a return value.
https://gitlab.gnome.org/GNOME/mutter/issues/447
