e2e Tests: Add test for inserter drag-and-drop

[ockham]

GB 10.5.0 had a small regression related to the inserter's drag-and-drop feature (see #31319). Let's try adding some e2e test coverage for that feature (maybe to https://github.com/WordPress/gutenberg/blob/cec7a6817ac2ec37e1e7a3b314fee0b909e7bd7d/packages/e2e-tests/specs/editor/various/inserting-blocks.test.js?).

Note that it has been previously thought to be impossible to cover drag-and-drop behavior with an e2e test. However, there is some prior art for blocks' drag-and-drop feature, see #26869.

[talldan]

Puppeteer now seems to support drag and drop (v10.1.0):
puppeteer/puppeteer#7150

However, I can't get it to work 😄

edit: got it working. The bit I was missing is that you have to do await page.setDragInterception( true ); before any drag and drop.

[kevin940726]

I can work on this next, as now we can also test dragging files in Playwright too (#42722).