Add slider to resize height of plot widget and cursor info box (XYZ, detectorID etc.) on LHS of instrument view

[RichardWaiteSTFC]

Is your feature request related to a problem? Please describe. WISH find it difficult to read the RTP of the cursor as too much space is given to the plot widget, which then has a elongated aspect ratio.

Describe the solution you'd like Add a slider to adjust the heights of these widgets

[stale[bot]]

This issue has been automatically marked as stale because it has not had activity in 6 months. It will be closed in 7 days if no further activity occurs. Allowing issues to close as stale helps us filter out issues which can wait for future development time. All issues closed by stale bot act like normal issues; they can be searched for, commented on or reopened at any point. If you'd like a closed stale issue to be considered, feel free to either re-open the issue directly or contact a developer. To extend the lifetime of an issue please comment below, it helps us see that this is still affecting you and you want it fixed in the near-future. Extending the lifetime of an issue may cause the development team to prioritise it over other issues, which may be closed as stale instead.

[RichardWaiteSTFC]

Re-opening this as WISH specifically requested it. Putting milestone 6.4 so doesn't get lost.