When the dialog is displayed, span the RDM iframe to the bottom row so it overlaps the browser stack,
as well as a potential bottom-docked DevTools toolbox.
We also need to adjust the z-index so it's displayed on top of the browser stack.
Finally, we set the `accomodate-ua` class on the .browserContainer element, and
use it to udpate the `--rdm-toolbar-height` variable, that we then use to set
the grid row's height; this way the row is always the same height, even when
we open the dialog (if we wouldn't do that, the row would grow, and we wouldn't
have the same space between the RDM toolbar and the content page).
Differential Revision: https://phabricator.services.mozilla.com/D317419
Nicolas Chevobbe
07c342e3e5