Plot legend enable/disable does not persist between plot draws (e.g. fit runs)

[pbeaucage]

Describe the bug
#1523 re-added a context menu toggle for visibility of the legend in a plot; however, that toggle just uses matplotlib methods to enable/disable the legend rather than using the internal Plotter class variables, which means that the visibility setting does not persist between re-draws of the plot during, for example, runs of a fit.

This tiles with other bugs such as #1337 on Mac and #2012 more generally to make 5.x versions often unusable with long filenames on Macs, since the legend obstructs the plot and one cannot turn it off without tediously clicking it off every time a fit variable is changed.

To Reproduce
Steps to reproduce the behavior:

1. Generate a plot from e.g. the fitting perspective
2. Toggle legend off using context menu
3. Perform an action (e.g. run a fit) that re-draws the plot.
4. Legend appearance will revert to on regardless of prior setting.

Expected behavior
Legend appearance/disappearance should follow previous plot interactions.

SasView version (please complete the following information):

• Version: 5.0.5

Operating system (please complete the following information):

• OS: Mac 12.5.1