There are extensive places in the code where we convert between the client
rectangle and the frame rectangle. Instead of manually doing it use
new helper functions on MetaWindow and the existing meta_window_get_outer_rect().

This fixes a number of bugs where the computation was being done incorrectly,
most of these bugs are with the recently added custom frame extents, but
some relate to invisible borders or even simply to confusion between the
window and frame rectangle.

Switch the placement code to place the frame rectangle rather
than the client window - this simplifies things considerably.

https://bugzilla.gnome.org/show_bug.cgi?id=707194