Add UTF-8 quoted path literals

[lukewilliamboswell]

Summary

• add a Utf8(Str) path representation for quoted literals
• add Path.utf8 and Path.from_quote, and thread Utf8 through path operations/raw conversion
• expand package and example tests for existing Unix/Windows behavior plus new quoted literal behavior

Testing

• roc fmt --check package examples
• roc check package/main.roc
• roc test package/main.roc
• ci/all_tests.sh