Background:
The advanced toolbar (add additional templates, add wikitext, move up/down, remove part) is only useful when there is multi-part content. In a typical single template editing situation they cause significant confusion. We will leave the toolbar as is, but hide when it is not needed and show when it is useful.

Requirements

• Implement behind a feature flag with:
  • T272368: Add checkboxes to param list sidebar in VE TemplateDialog
  • T272481: Add parameter search to sidebar of VE TemplateDialog
  • T272487: New input for undocumented parameters
• When inserting a template or editing a single template, the tool bar is hidden
• When editing pre-existing multi-part, linked content, the tool bar is shown
• When editing pre-existing multi-part content, the tool bar is shown even if the user removes all but one content/template i.e. the state of showing/hiding toolbar does not change within an editing session. If the user saves and reopens the dialog, it would be treated as a single template editing session and the toolbar would be hidden.
• Each button functions as they currently do:
  • Puzzle icon brings up template search and when template is chosen from the dropdown is added to the sidebar and is editable
  • [[ ]] icon adds wikitext/content field to the main dialog and sidebar list
  • Move up/down arrows allow to move content order in relation to each other. Current disabling behavior remains the same.
  • Trashcan removes content
• Remove the Parameter icon, the option's updated behaviour is addressed in this ticket T272487: New input for undocumented parameters
• After removing parameter icon, adjust spacing of icons as shown in the specs below
• Rename 'Content' component to 'Wikitext'
• When the toolbar is hidden the space at the bottom should be gone
• Trashcan only works when template name or wikitext titles in the sidebar are focused. When parameters are in focus, the trashcan is disabled.

For reference
Current toolbar:

Mock:

Note: ellipsis/menu implemented in the prototype is not being used in the final design. Some of the above functions were included there but are no longer being moved. See prototype ticket for reference: T263414: Change behaviour for adding/removing templates