Refactor <BlockTools /> to be exported with all Block Toolbar Functionality

[jeryj]

Follow-up to #55787

What problem does this address?

The <BlockToolbar /> component should be able to be used directly with all of the functionality of the Block Toolbar. In its currents state, the <BlockToolbar /> component does not have many of the accessibility improvements and keyboard navigation features. Those are implemented via <NavigableToolbar /> within <BlockContextualToolbar />.

What is your proposed solution?

• Refactor <BlockToolbar /> to include the features of <BlockContextualToolbar />. This would remove <BlockContextualToobar />
• Remove <BlockContextualToobar /> and its private-api export
• Replace usage of <BlockContextualToobar /> in edit-site, edit-post, edit-widget, etc headers with `
• Refactor <SelectedBlockTools /> to use <BlockToolbar /> directly.
• Rename <SelectedBlockTools /> to something that indicates its true purpose -- making the <BlockToolbar /> into a floating popover. Something like, <FloatingBlockToolbar /> or <BlockToolbarPopover />.

[jeryj]

Closed by #56335