Added type hints

[radarhere]

Suggestions for python-pillow#8032

• Added some type hints to tests to go with the ImageGrab changes
• Removed a cast in Image.py that isn't needed
• Used a new variable in ImageGrab instead of casting, which I think is simpler

[nulano]

I'm not too sure about this change.
Although mypy does not complain either way, I can see a warning in PyCharm without the cast.
Running mypy with --strict prints a warning that could explain why it (incorrectly) does not error without the cast:

src\PIL\Image.py:1158: error: Item "None" of "Optional[Any]" has no attribute
"getcolor"  [union-attr]
    ...                   new_im.info["transparency"] = new_im.palette.getcol...
                                                        ^~~~~~~~~~~~~~~~~~~~~~~

I suspect that the warning is only skipped because mypy doesn't realize that new_im.palette is an ImagePalette because it is set within an if block (unlike the cast above which is not in a nested if block).

Edit: clarify wording

[radarhere]

I've created python-pillow#8167, where I give up on the idea of requiring getcolor() to have a length of exactly 3 or 4. If that is merged, then my next suggestion would be radarhere@dfc1b0f

But I am keen to get python-pillow#8032 in for this release, so at any stage if you say 'Hey, let's merge it as it is and debate this later', we absolutely can.

[nulano]

Yeah, I'd prefer to discuss this commit separately then.

Could you rebase to remove the commit so I can merge the rest of this PR?
And put it in a separate PR to the main repo once python-pillow#8032 and python-pillow#8167 are merged?

[radarhere]

Sure. I've removed the commit.

[radarhere]

Both the PRs have been merged, so I've created python-pillow#8169

[nulano]

Thanks