ToolsPanel: Prevent tools panel menu increasing empty panel height

[aaronrobertshaw]

Description

This PR tweaks the ToolsPanel so that an empty panel's height is consistent with a collapsed panel.

This issue was raised through the review process of switch the border panel over to use the ToolsPanel.

See: #33743 (comment)

How has this been tested?

1. Via the Storybook and inspecting the empty panel's height is 49px
   • npm run storybook:dev
   • Visit storybook example containing empty panel
   • Inspect via dev tools
2. Cherry-picking this change onto the Border panel switch to ToolsPanel PR
   • Open block editor, add group block, and select it.
   • Confirm the collapsed color panel's height is the same as the empty border panel's.

Screenshots

Types of changes

Enhancement.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[jasmussen]

Thank you!

[ciampo]

Thank you @aaronrobertshaw ! Could you add a little CHANGELOG entry before merging?

Otherwise LGTM 🚀