Implement FigureManager.resize for macosx backend - #16992

Tagging 3.3 since the underlying issue is tagged 3.3. Would be nice to get the issue closed.

Just given this a spin and it seems to work well. The only thing I've noticed is if I resize the window to have zero height, I get a bunch of messages like:

  File "/Users/dstansby/github/matplotlib/lib/matplotlib/figure.py", line 879, in set_size_inches
    raise ValueError(f'figure size must be positive finite not {size}')
ValueError: figure size must be positive finite not [ 5.65 -0.34]
Traceback (most recent call last):
  File "/Users/dstansby/github/matplotlib/lib/matplotlib/backends/backend_macosx.py", line 84, in resize
    forward=False)
  File "/Users/dstansby/github/matplotlib/lib/matplotlib/figure.py", line 879, in set_size_inches
    raise ValueError(f'figure size must be positive finite not {size}')
ValueError: figure size must be positive finite not [ 5.6  -0.19]

@dstansby We currently expect figures to have a finite height and width. However that may change, see #17093 (comment).

In other backends (WebAgg, specifically), there are minimum sizes on the window so you can't do that.

Yeah, I'm guessing the backend should enforce >0 figure height and width.

So is that a requested change on this PR?

I think it would be good to enforce a finite size for this PR, so that we can get it still into 3.3. There are considerations elsewhere to drop that limitations, but that needs additional changes in the code.

How does this interact with

#17084 and
#17263 ?

@tacaswell Should be no interaction between this and either of those other two.

@timhoffm To be clear, this PR does not make the figure size must be positive finite messages newly possible. I can get those today with master just fine:

Traceback (most recent call last):
  File "/Users/rmay/repos/matplotlib/lib/matplotlib/backends/backend_macosx.py", line 80, in resize
    self.figure.set_size_inches(width * self._device_scale,
  File "/Users/rmay/repos/matplotlib/lib/matplotlib/figure.py", line 879, in set_size_inches
    raise ValueError(f'figure size must be positive finite not {size}')
ValueError: figure size must be positive finite not [ 0.73 -0.24]
Traceback (most recent call last):
  File "/Users/rmay/repos/matplotlib/lib/matplotlib/backends/backend_macosx.py", line 80, in resize
    self.figure.set_size_inches(width * self._device_scale,
  File "/Users/rmay/repos/matplotlib/lib/matplotlib/figure.py", line 879, in set_size_inches
    raise ValueError(f'figure size must be positive finite not {size}')
ValueError: figure size must be positive finite not [ 0.73 -0.35]

(just grab the upper right corner and drag down and to the left past the lower left corner.)

I can do it if strictly necessary, but it's not a new issue introduced by this PR.

I'm going to merge then; finite size requirements can be a separate new PR.