Ctrl+Shift+Arrow (and Shift+Arrow, Shift+PageUp/PageDown, Alt+Shift+PageUp/PageDown,
Ctrl+Shift+Home/End, Shift+Home) extend the selection by moving its far corner while the
active cell stays on the anchor. After the move the grid set `ensure_visible`, but the
scroll-into-view step in `grid::show` always targeted `selection.active`, which is the
anchor and is already on screen. So the view never followed the extension past the last
visible row or column.
The keyboard extension paths now also set `GridState::reveal_moving_end`, and the
ensure-visible step then scrolls to `Selection::moving_end()`, the corner opposite the
anchor. `selection.move` now uses that same helper (it had the logic inline) to find where
an extension starts. Other ensure-visible callers (Go To, Name Box, plain moves) still
reveal the active cell.
Regression test: crates/ui-egui/tests/selection_scroll.rs drives Ctrl+Shift+Up/Down/
Left/Right, Shift+Down/Right and Ctrl+Shift+Home/End through real egui key events and
checks that the moving end ends up on screen while the anchor and active cell stay put.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
