Adwaita: overshoot style tweaks

Trying to make it visible on the dark variant.
Drop unused variables

Keeps the compiler happy.
Make overlay scrollbar fading interruptible

When the pointer starts hovering the scrollbar after it already
started fading out, interrupt the fade and keep the scrollbar
around.
Adwaita: more overshoot tweakings and typo fix
Adwaita: popover scss cleanup
mir: fix compilation in mirscreen
mir: handle more surface types
Adwaita: :selected cleanup and rationalization
entry: remove osd style class from touch selection popover

The touch-selection class is sufficient since that needs special
casing whatever.
textview: remove osd style class from touch selection popover

The touch-selection class is sufficient since that needs special
casing whatever.
Adwaita: no border radius for GtkTreeView:selected
GtkPopoverMenu: Implement forall

This is required to make glade work.
Make gtk_container_remove work on popover menus

Extend the hack we have in place for composite containers to
GtkPopoverMenu.
mir: Require mirclient >= 0.9.0

Recent changes to the Mir backend require an unreleased version.
mir: invert scrolling delta
mir: fix typo in GDK_IS_WINDOW_MIR definition
scrolledwindow: Only render background/frame on the widget window

Otherwise it is rendered too on each indicator window, possibly bringing
in an unintended opaque background there. Better seen with git show -b.
scrolledwindow: Avoid too frequent redraws of scrollbars

When overshooting through touchpad kinetic scrolling, the scrollbar remains
mostly static as it already hit a boundary. However, the fade in/out checks
are constantly run during scroll events, causing needless redraws in this
specific case.
mir: update surface type based on events
GtkMenuSectionBox: Add tooltip to iconic buttons