Opening the panel from the Window menu worked, but collapsing the dock did not
show it: `ICON_PANELS` only registers a panel (so `window.panel` finds it) while
`ICON_PANEL_GROUPS` is what the collapsed column actually draws, and `variables`
was in the first list only. Sixteen panels are registered without a group; for
the ones meant to live in the column, the entry in `ICON_PANELS` alone is not
enough.
`variables` gets a row of its own at the bottom of the column, where the
reference app keeps it. Both lists now say which is which, so the next panel
does not repeat this, and a test asserts a registered panel reaches the column
(it fails without the group entry) and that every grouped id names a registered
panel with an icon.
`floating.rs`'s icon test counted the column's icons, which only means
"one left" while the column is tall enough to show them all — past that, one
scrolling into view replaces the one that left. It runs on a window tall enough
for every icon now, and checks the count is the number of registered groups'
icons rather than a number that happens to pass.
Dragging a panel into the icon column still doesn't work, and is not something
this PR changes: tearing a panel off makes it float, for every panel. Docking it
back into the column would be a dock feature of its own.
cargo xtask ci: all 7 steps pass on Rust 1.99.
06dbe5b1e8