Fixes #66277

What?

After #61331 the size of the X close button of various sidebar panels is unnecessarily too small and inconsistent with other similar buttons.

Why?

For better usability and accessibility, the target size should always be as big as possibile.

How?

Increases the button size to compact and adjusts alignments where necessary.

Testing Instructions

• Go to the Site editor.
• Open the Styles panel.
• Observe the size of the buttons in the panel header is now consistent and the X close button uses the 'compact' size (32 by 32 pixels).
• Observe the gap between the buttons is consistent.
• Observe the X close button is horizontally aligned with the ellipsis button in the top bar.
• Install and activate a plugin that adds a plugins panel e.g. Yoast SEO.
• Go to the Post editor.
• Open the plugin panel and observe the 'Pin / Unpin' button and the X close button use the 'compact' size (32 by 32 pixels).
• Open the post/block settings panel and observe the X close button uses the 'compact' size (32 by 32 pixels).
• Open the main inserter and observe the X close button uses the 'compact' size (32 by 32 pixels).
• Same for the List View panel.
• Set Twenty Twenty-One as the active theme.
• Go to the Widgets page.
• Observe the size and alignment of the main inserter and the List view X close buttons are consistent.
• Aside: Observe the right padding of the widgets editor top bar is now consistent with the one of the other two editors.

Testing Instructions for Keyboard

Screenshots or screencast