Enhancement: Increase target size of checkboxes on Forms

### Impacted plugin

Jetpack

### What

It's too easy to deselect multiple items when you're checking all form responses

### How

The click target for Jetpack Form responses is the checkbox only, if you miss the checkbox slightly it's incredibly frustrating as it selects the item you've clicked on, but deselects all others.

Additionally, Shift+click to select a selection of checkboxes is not supported (as WordPress Core list tables do)

https://github.com/user-attachments/assets/22ef92b1-7e0d-403f-b2d8-94816e5bedfe

Start at the Jetpack Form responses interface and trace how checkbox clicks select or deselect items. Confirm the current single-click behavior, then verify that the completed change gives each checkbox a larger click target and supports Shift-click range selection without losing existing selections.

Written by the indexing model from the issue text.