Ability to set Action on StatusItem post creation

[tznind]

Is your feature request related to a problem? Please describe.

Action is now get only. This presents a problem in TerminalGuiDesigner where event handlers have to be declared by users within the .cs file (while designed views are constructed in .Designer.cs)

Describe the solution you'd like
Add set keyword to Action

Describe alternatives you've considered
None

Additional context
The API docs seem to indicate that this was possible at some point. Or it was intended to be the case.

[tig]

See #3073

But we should fix this issue short term.

[tig]

Fixed with new StatusBar