External Media: add ability to bulk-select with the shift key

### Impacted plugin

Jetpack

### What

In the external media, you currently do not have the controls you would typically have in a gallery selection, like the core media modal. Let's add that option to be consistent.

### How

Here is a quick video to show you the differences between the shift key in the core media modal, vs. the External Media modal:

https://user-images.githubusercontent.com/426388/187920105-6574cc2d-447c-47f1-a656-53e0acdd300d.mov

The issue identifies the External Media modal and the core media modal as the behavior to compare, but names no files, tests, or entry points. Start by locating the External Media selection UI and comparing it with the core modal's shift-key behavior; done means users can bulk-select a contiguous range consistently.

Written by the indexing model from the issue text.