Computes the vblank duration from mode timings. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1762>
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1737>
They are not strictly related to any of the KMS objects, and should be reusable without adding a dependency on the non-meta-kms-* files in meta-kms-*. https://gitlab.gnome.org/GNOME/mutter/issues/548 https://gitlab.gnome.org/GNOME/mutter/merge_requests/525