unexpected highlighting behaviour when copying a large selection

[cldougl]

First reported #253 (comment) There's some unexpected highlighting behaviour when copying a large selection (i can move this to a separate issue if we want to address after this pr/during clean up).

• select a cell
  -scroll down (so selected cell is no longer displayed)
• shift and select a new cell to select a range
• see unexpected highlighting (blue in gif)
• copy and paste works as expected

[Marc-Andre-Rivet]

This is a new issue introduced by the virtualization -- by the time the user scrolls to the destination cell, the starting cell does not exist anymore, causing the selection to be in a weird place / out of scope.