tests: add insertBlockAndWaitForSelector utility

[flootr]

What?

Add a insertBlockAndWaitForSelector utility to the e2e test utils for playwright package which inserts a block and then waits for a given selector to be visible.

Why?

The idea came up when I started working on fixing e2e tests in #55585 which attempts to lazy load edit functions of blocks. After using insertBlock we have to wait for a certain selector to be visible, otherwise some of the tests fail which attempt to e.g. type something into a block which isn't there yet.

In 50cd450 you can see this might result in a lot of repetitive code which this util tries to abstract away. It's probably not suitable for all block insertions done in those tests but should cover a fair bit.

How?

The @wordpress/e2e-test-utils-playwright exports a bunch of methods and we're adding insertBlockAndWaitForSelector to it.

Testing Instructions

Testing Instructions for Keyboard

none

Screenshots or screencast

none

[github-actions]

Flaky tests detected in 0c1f48e.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/7033437691
📝 Reported issues:

• [Flaky Test] should partially select with shift + click (@webkit) #53524 in /test/e2e/specs/editor/various/multi-block-selection.spec.js