Add heading title and optional sub-header to all panels

[afercia]

Description

Splitting this out from conversation and ideas shared on #61553

Cc @jeryj @joedolson

The conversation on #61553 surfaced a few points where the current design doesn't seem to clarify enough what the purpose of the editor panels is. On top of that, the order of some controls in the panels header isn't ideal, especially when the header contains additional controls e.g. the Styls panel.

Visible titles for all panels

Any panel is basically a section of content.

In a good UI, any section of content should be clearly identify what it is about. Headings for all the panels would help with that.

For an example of a panel that, over time, has become a little disorienting see the discussion about the 'block inserter' panel on #61483. With the addition of Patterns and Media, the 'Block Inserter' is not just about blocks any longer. The current labeling and names are out of date. That panel is now more a 'Library' with various content types that can be added: Blocks, Patterns, Media.

I'd argue that when an UI section doesn't clarify what it is about, there is a problem of clarity and information architecture in the first place. Updating all the labels with a more meaningful naming and adding a heading would solve the clarity issue.

I took some time to run a little research. Far from pretending to be an exhaustive research, here's some examples well known web applications and software that user visible titles for their panels:

Google Docs

• Document outline panel
• Open a file: Recent and My Drive tabs - their panels have visible titles
• Approvals
• Version history
• Tools > Citations
• Tools > Tasks
• Tools > Variables
• Tools > Line Numbers
• Tools > Linked Objects
• Tools > Dictionary
• Insert > Image > Drive
• Insert > Image > Photos
• etc.

Google Drive (right side panels)

• Calendar
• keep
• Tasks
• Contacts

Gmail

• some of the panels have visible titles

Microsoft Teams web

• most of the panels have visible titles

WhatsApp web

• most of the panels have visible titles

Wix

• Inbox
• Notifications
• New Releases
• Write block post page:
  • Add
  • Post settings
  • SEO settings
  • Subscription plans
  • Translate
  • Approvals
  • Create with AI

Figma

• most of the panels have visible titles

Canva

• most of the panels have visible titles

Instead, in the editor panel titles are an exception. For example. the Styles panel does have a visible title. Most of the other panels don't.

Visible titles appears to be, in a way, an industry standard. I'd like to propose to add visible, consistent, titles to all the editor panels:

• Navigation panel
• Main Inserter
• List View
• Inspector
• Styles panel
• Plugins panel
• Any more panel I may be missing...

Visible titles would also allow to solve the issue of the X close button placement.
A panel header would only contain: the title, followed ny the Close button.

Optional sub-header for additional controls

In some cases, the editor panel headers contain additional controls. See for example the Styles panel and the Plugins panel.
That's not ideal as it is, in the first place, inconsistent.
Also, the logical order isn't meaningful, see hte Styles panel.
Also important: when the 'Show button text labels' preference is enabled, those controls in the panel header simply don't have enough space to show their text and are prone to layout breakage. It appeares the original design that added those buttons in the panel header didn't take into consideration 'Show button text labels' at all. See #61761. Those buttons shouldn't be placed there in the first place.

Step-by-step reproduction instructions

• Explore all the pabels in the editor e.g.:
• Navigation panel
• Main Inserter
• List View
• Inspector
• Styles panel
• Plugins panel
• Any more panel I may be missing...
• Observe the Styles panel and the Plugins panel do have visible titles, the other ones don't.
• Open the Styles panel.
• Enable the 'Show button text labels' preference.
• Observe there's very limited space in the panel header to show these buttons text.
• Test with languages other than English that may provide longer strings e.g. Gernab, Spanish, Italian.

Screenshots, screen recording, code snippet

No response

Environment info

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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