Use fixtures instead of classes in test_imagefont

[nulano]

Changes proposed in this pull request:

• Use fixtures instead of classes to make test_imagefont.py a bit easier to read.
• Parameterize tests for TransposedFont.
• Combine test_find_linux_font and test_find_macos_font into a single parameterized test.

[hugovk]

One quick suggestion, not reviewed it all yet.

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For next time: it would probably be easier to review this as separate commits, rather than a big, single change. Don't worry about it this time, unless it's easy to re-do. Thanks!

[nulano]

For next time: it would probably be easier to review this as separate commits, rather than a big, single change.

Just in case you aren't aware of it, I find the split view with "Hide whitespace" enabled the easiest to read for reviewing this:

Don't worry about it this time, unless it's easy to re-do. Thanks!

Not easy to split for this PR, but I will try to make smaller commits for next time.

[hugovk]

Thanks!