[whatwg/url] Report a validation error for IPv4 addresses from non-ASCII input (PR #925)

## Summary

- The domain parser silently maps fullwidth digits, ideographic dots, superscripts, circled digits, and ignored code points into ASCII digits and dots. When the mapped result ends in a number, the host parser IPv4-parses it cleanly with no validation error, yet such input is neither a valid IPv4-address string nor a valid domain string (e.g., `https://①.②.③.④`, `https://1。2。3。4`, `https://².2.3.4`).
- Adds a new `IPv4-non-ASCII-input` validation error, fired when `asciiDomain` ends in a number and the pre-ToASCII `domain` is not an ASCII string.
- Helps with #704.

## Test plan

- [ ] Confirm the alignment against the differential fuzzer (https://gist.github.com/domenic/c2285ead47ddd80e1f5ae98062e41e57).
- [ ] Verify implementations can plumb the new validation error through.


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You can view, comment on, or merge this pull request online at:

  https://github.com/whatwg/url/pull/925

-- Commit Summary --

  * Report a validation error for IPv4 addresses from non-ASCII input

-- File Changes --

    M url.bs (18)

-- Patch Links --

https://github.com/whatwg/url/pull/925.patch
https://github.com/whatwg/url/pull/925.diff

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