Dashboards: PanelChrome - remove untitled placeholder and add border when panel is transparent

[axelavargas]

What is this feature?

During the redesign of the panel header, we decided to add a placeholder name, "Untitled". This decision was based on feedback about the menu not being discoverable and the drag icon conflicting with the menu icon, which looked like nine dots.
After receiving both internal and external feedback, we decided to remove this placeholder. It was causing confusion and wasn't adding enough value, especially since the original issues were addressed differently.

This PR addresses two issues:

1. It removes the "Untitled" placeholder.

Before	After

2. It adds a border on hover when the panel is transparent.

Before	After
Before-hoverWhenTransparentBackground.mp4	hoverWhenTransparentBackground.mp4

Why do we need this feature?
Removes the current confusion about panels without headers.

Who is this feature for?

Everyone

Which issue(s) does this PR fix?:

Fixes #72978, #70510

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.

[juanicabanas]

LGTM! I loved the border change 🚀

[craftzneko]

The border around a panel when transparent is kind of a pain for my use case. I have multiple panels (using dynamic text plugin) that pass data between them and the overall look is off a portal style page. I feel this should be an option that is selectable in properties. Also the pop up Untitled (or even just the move icon) should not really appear for users who have no permissions to edit the page, why would they be shown options they cant use? I know this has been asked so many times over the years but sometimes we just want to present a dashboard with no interactions except for the interactions we design. For others looking to remove the border and the panel menu. If you are using a plugin that allows you to directly add JS (such as the amazing Dynamic Text) you can add this (wrap it in a docready function so the page loads first)

  let elements = document.querySelectorAll('[class*="panel-container-panel-transparent-container"]');

  elements.forEach(element => {
    element.style.border = 'none';
  });

  let hoverElements = document.querySelectorAll('[class*="hover-container-widget"]');

  hoverElements.forEach(element => {
    element.style.visibility = 'hidden';
  });