Change to allow WaveFile and MP3Decoder to accept a file path

[snkYmkrct]

Hello 🐈‍⬛ 🐈‍⬛

I made the changes required by issue #5713 , following the pattern used with OnDiskBitmap.
WaveFile and MP3Decoder can now accept either an open file pointer, or a string file path as parameter.

Changes tested on the Adafruit Pygamer and Pyportal Titano.

Please let me know if this looks good.

[jepler]

Thank you! This looks very simple and sensible as a change. I do have a note about the documentation -- I only added a single comment but it looks like it applies equally to wave and mp3 sections.

In addition to that, if it is easy can also see whether you can make assigning a string to the mp3.file property can be made to work? If it is not easy, we can leave it for a future PR.

[snkYmkrct]

@jepler
I made the requested documentation changes.

I am a beginner at working with something like CircuitPython core (first core contribution actually), so I can't speak to how easy it would be to add a string to the mp3.file, but I can definitely look into it.

[jepler]

Thank you! It looks good now. Changing how the mp3decoder's file attribute works can be done later.

[snkYmkrct]

Thank you! 😸