closes #26477 ENH: Add interpolation_stage in qt figureoptions

[Tsufael]

I'm not sure if demonstration in an [example] and writing tests for this PR applies.

Closes #26477

PR summary

Add getter for image interpolation_stage;
Add interpolation_stage selector for images in qt figureoptions.

The getter was added to check what option should be selected when the menu is opened.

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines

[melissawm]

Hello @Tsufael - just noting that if you want this to be reviewed, make sure you mark it as "Ready for review". Thanks!

[oscargus]

I do not think that the figure options dialog is currently tested.

You will need to add something like

def get_interpolation_stage(self) -> Literal["data", "rgba"]: ...

to image.pyi (ideally above set_interpolation_stage) to get rid of the mypy error (not clear to me what the role of 'none' is here though).

For the PR it looks OK, but will have to try it out manually before I can fully tell/approve.

[QuLogic]

This appears to work as far as I can tell. I rebased and added the type hint as this seems almost complete.

[QuLogic]

One more rebase to fix linting and docs.

[dstansby]

Checked the figure options locally, and it works. Anyone can merge if/when CI passes.

Thanks for your first PR to Matplotlib!