PR: Add minimum version check for Qt6 >=6.2.0

[CAM-Gerlach]

Per the discussion in #233 , adds a minimum version check for Qt6 and each binding to ensure they are at least version 6.2.0 or higher, since we don't officially support anything under that. Also, refactors the constants a bit accordingly.

Closes #233 (again)

[ccordoba12]

Looks good to me, thanks @CAM-Gerlach!

[kumattau]

@CAM-Gerlach, @ccordoba12,

How about introducing PYQT5_VERSION, PYSIDE2_VERSION, PYQT6_VERSION and PYSIDE6_VERSION ?

l think,

parse(PYQT5_VERSION) <　parse(PYQT5_VERSION_MIN)

is better than

parse(PYQT_VERSION) < parse(PYQT5_VERSION_MIN)

and others are the same.

[CAM-Gerlach]

Hmm, thanks for the suggestion @kumattau . My take is that it might look a little better in a few parts of the warning check code, but I'm not sure that a bit of internal-only aesthetics is worth introducing even more new package-top-level public constants (that would have to be changed with QtPy versions that added/removed binding support) which are rather redundant to each other (since only one is going to be defined at a time) and the need to define and check them would add further code complexity to a (difficult to reliably unit test) warnings check. Additionally, on the aesthetics front, adding that one addition character would push several of the lines over the 79 char limit, making it even longer, less consistent and harder to read at a glance.

@dalthviz , what do you think?

[kumattau]

Let me explain the background of my proposal in a little more detail.
First, PYQT_VERSION and PYSIDE_VERSION are expected to be public APIs for users because these don't start with an underscore.

In the current API, the following simply comparison

parse(PYQT_VERSION) < parse(PYQT6_VERSION_MIN)

is incorrect usage (parse('6') <= parse(PYQT_VERSION) is required before comparison ), but it is difficult for users to understand this.

The related public APIs is as follows.

• QT_API environment variable
  pyqt5, pyside2, pyqt6 or pyside6 is set

• PYQT5, PYSIDE2, PYSIDE2, PYSIDE6
  corresponding the above QT_API, the only one of these constants is set to True, others are set to False

By introducing PYQT5_VERSION, PYSIDE2_VERSION, PYQT6_VERSION and PYSIDE6_VERSION, XXX_VERSIONs become the same behavior as PYQT5, PYSIDE2, PYSIDE2, PYSIDE6 and users can use XXX_VERSIONs without mistake.

Additionaly, I think introducing QT5_VERSION and QT6_VERSION is better from the API consistency perspective.

The above is my personal opinion, and of course, I respect the judgment of the spyder team.

[dalthviz]

Thanks @CAM-Gerlach for working on this! I left some comments/suggestions/questions to:

• Simplify the warning message
• Add more carity to the validation on Qt6 taking into account the comments of @kumattau (thanks for taking the time to check this and raising your concerns by the way 👍)

[dalthviz]

Thanks @CAM-Gerlach for working on this! LGTM 👍

Also, thanks @kumattau for the feedback! 👍