Add control to exit presentation mode

__Proposal:__
When a dashboard is in presentation mode, it is confusing how to exit. Add an ever-present exit button to the top of the dashboard.

__Current behavior:__
Currently, the only way to exit presentation mode is the `esc` key. A notification fires on entering presentation mode to inform the user of this interaction.

Ref: Issue #10772

__Desired behavior:__
- Keep the current interaction and add an ever-present exit button to the top of the dashboard.

__Alternatives considered:__
- Add permanent help text to inform the user of the interaction.
- Add right-click interaction to exit presentation mode.

Start by locating the dashboard presentation-mode entry point and the existing Esc-key exit interaction. Add an always-visible exit control at the top while preserving the current keyboard interaction, then verify that entering presentation mode and both exit paths behave as described.

Written by the indexing model from the issue text.