overviewControls: Limit Dash height to 15% of the overview's

overviewControls: Limit Dash height to 15% of the overview's

Back when the Dash was vertical, the size of each item was calculated
solely based on the available height. After making the Dash horizontal,
this was swapped by the available width. However, when the height of the
Dash decreases, the current code results in never scaling them up ever
again.

Fix that by making ControlsManagerLayout explicitly pass the maximum Dash
sizes. Remove the 'notify::width' handler that served the same purpose.

Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3651

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1638>