Avoid more occurrences of the term 'sidebar' in user-facing strings

[afercia]

Description

In #49613 and #49614 the term 'sidebar' was removed from most of the user-facing text / labels / names.

There is also an issue open to remove the term 'sidebar' from the Handbook, see #57546

In the meantime. I noticed that new occurrences of the term 'sidebar' are still in the codebase and they should be replaced by a more generic, non-biased, term such as 'panel'.

To recap the main reasons why the term 'sidebar' should be avoided:

• The whole concept of 'sidebar' is extraneous to blind screen reader users. The term 'sidebar' is a positional reference, as it refers to something that is placed on a 'side'. As a blind user, it doesn't help me to know whether a section of the user interface is visually placed on the side, top, bottom or in any other spot of the screen.
• Ideally, UI sections should be named based on their functionality rather than on their visual aspect. Same applies for components.
• On small screens, most of these UI sections aren't 'sidebars' any longer. They're more full-width overlay panels so that the term 'sidebar' isn't accurate in this case.
• When translated, the term 'sidebar' is generally way longer than in English and that doesn't help readability.

It would be great to educate all contributors to not use the term 'sidebar' other than for internal purposes. It should never be used in user-facing strings or public documentation.

Step-by-step reproduction instructions

Occurrences found in the codebase as of May 2024:

• _e( 'You can change the amount of columns in your galleries by dragging a slider in the block inspector in the sidebar.', 'gutenberg' );
• label: __( 'Toggle settings sidebar' ) - in the commands palette, common commands
• label: __( 'Toggle settings sidebar' ) - in the commands palette, edit mode commands
• el( PanelBody, {}, __( 'My sidebar content' ) ) in the editor README, + 3 more occurrences
• description: __( 'Show or hide the Settings sidebar.' ), in the global keyboard shortcuts
• a few occurrences in the plugin sidebar docblock
• a few occurrences in the plugin sidebar more menu item docblock

Note; while the occurrences in the docblocks aren't technically user-facing, they do suggest to use the term 'sidebar' in user-facing strings. As such, they should be changes as well.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[n2erjo00]

@afercia There is new shiny PR which replaces sidebar usage