[FIX] GridOverlay: Prevent mousedown default when selecting range

When selecting a range in the grid and the composer is open, passing
your selection around the composer will see its content selected as if
we were actually selecting text inside the composer.

This behaviour is a direct effect of the default behaviour of the
mousedown event that starts the selection. Since the focus is kept on
the composer at all times, the browser behaves as if we had clicked on
the composer itself even if from a user point of view, it makes little
sense.

closes #7493

Task: 5344285
Signed-off-by: Lucas Lefèvre (lul) <lul@odoo.com>

Author: rrahir

src/components/grid_overlay/grid_overlay.ts

@@ -228,6 +228,7 @@ export class GridOverlay extends Component<Props, SpreadsheetChildEnv> {
       // not main button, probably a context menu
       return;
     }
+    ev.preventDefault();
     const [col, row] = this.getCartesianCoordinates(ev);
     this.props.onCellClicked(col, row, {
       expandZone: ev.shiftKey,