[path_parsing] Initial import

[stuartmorgan-g]

Imports https://github.com/dnfield/dart_path_parsing into this repository, with history, and updates it to follow repository conventions:

• Updates minimum SDK support to match our minimum
• Switches to repository analysis options, fixing or suppressing all resulting warnings
• Standardizes pubspec.yaml to follow our style/conventions
• Removes the use of pubspec.lock, per repo conventions

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[stuartmorgan-g]

@zanderso Would you like to edit the README to add a note?

Also, currently we use CODEOWNERS in this repo; who should I list for this and the follow-up packages?

[zanderso]

Yes, I'll edit the README. Working on the text, but I think this PR doesn't need to block on it?

A while back, @domesticmouse volunteered to be the owner for these for the purposes of mechanical updates with more involved issues in flutter_svg being owned by @jonahwilliams and the engine team.