Corrected some docstrings that are using enumeration parameters

[hecent]

Converted things like Dither.FLOYDSTEINBERG to PIL.Image.Dither.FLOYDSTEINBERG to match other docstrings and to as that is the correct code.

[hugovk]

Thanks for the PR, here's an example:

Before	After

In both cases, they link to the same things. For example, the first link:

• https://pillow.readthedocs.io/en/stable/reference/Image.html#PIL.Image.Quantize.MEDIANCUT
• https://pillow--6491.org.readthedocs.build/en/6491/reference/Image.html#PIL.Image.Quantize.MEDIANCUT

But the PR makes the links appear more verbose.

[hecent]

The PR was to make the links the same format as other docstrings like resize() or transform() and so that they better represent what you are actually supposed to write when passing the options as parameters:
If you didn't know better it seems as though they should be written as Image.quantize(method=Quantize.MEDIANCUT) from reading the docs (which I did), and is incorrect.

(https://pillow.readthedocs.io/en/stable/reference/Image.html)

[radarhere]

#6557 has been merged instead, resolving the inconsistency by replacing PIL.Image.Resampling.NEAREST with Resampling.NEAREST.