net/url: add URL.RawFragment, like RawPath

[rsc]

OpenAPI and JSONSchema do fancy things with the fragment including
funny path operations that distinguish between a literal / and an escaped %2f.
Just like happened with Path, the solution is probably to add RawFragment,
with the same semantics for Fragment/RawFragment as Path/RawPath.

/cc @mpvl

[rsc]

Adding to the proposal minutes. This seems fairly unobjectionable given the precedent set by RawPath. If anyone thinks we shouldn't do this, please speak up. Thanks.

[rsc]

Based on the precedent from RawPath and the lack of any objections, this seems like a likely accept.

[rsc]

No change in consensus (still crickets here), so accepting.

[gopherbot]

Change https://golang.org/cl/227645 mentions this issue: net/url: add URL.RawFragment, URL.EscapedFragment