Wrap the always-visible textControl in a PanelBody so that it has the correct padding

[benlk]

Changes

This pull request makes the following changes:

• Wraps the non-advanced controls in a PanelBody element so that the Pym.js Child URL control doesn't overflow its container
• Bumps "Tested up to:" to 5.4.
• Starts changelog for the [next] release, which will likely be 1.3.2.4.

Before:

After:

Why

For #72, fixing a visual regression in WP 5.4

Testing/Questions

Features that this PR affects:

• the block inspector controls

Questions that need to be answered before merging:

• [x] Is this PR targeting the correct branch in this repository?
• [x] Does this work for the test cases provided in https://github.com/INN/pym-shortcode/blob/master/docs/maintainer-notes.md#testing-before-release ?

Steps to test this PR:

1. View a Pym.js Embeds block's sidebar controls under master, and under this branch.

[joshdarby]

@benlk Do you think we need to update the version number so we don't run into the issue we did when updating SCAIP?

[benlk]

We do need to do that, but I was going to do that in a separate PR.