This commit takes rfc8297 into account and introduces a newer code 103
HttpStatus value which uses `Early Hints` as the more correct reason
phrase, deprecating the outdated `CHECKPOINT` enum value for 103.
Additionally:
- `HttpStatus.valueOf(103)` will return the new enum value
- `HttpStatusCode#isSameCodeAs(HttpStatusCode)` is introduced to ease
comparison of deprecated enums vs their newer counterparts (or any
instance of a more generic `HttpStatusCode`) by comparing the integer
`value()`
- `HttpStatusTests` covers the new deprecation as well as the three
previously deprecated codes, including a check with the above new
method to ensure they have comparable integer values
Supersedes and Closes gh-27960
5de1460f88