Add `dev.py` implementing dev command shorthands

[ankith26]

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This is an attempt at simplifying the steps a pygame-ce dev has to do to get out a complete working change that passes our CI.

Some goals

• help new devs figure stuff out faster. This script does an auto-install of all dependencies needed, so virtually no setup is needed to run this script. For people who don't like the idea of a script messing with the global package space, this script also provides a flag to do everything inside a venv.
• make the dev workflow more efficient, with shorthand commands for all the common steps one usually needs.
• get everyone onboard the editable install strategy, with one convenient command.
• serve as a self-documenting system (with help commands)