Make HostResolver::AllProtocolEndpointsHaveEch() generic

So that we can call the function for both HostResolverEndpointResult
and ServiceEndpoint. This is a preparation for supporting ECH in
HttpStreamPool.

No behavior changes.

Bug: 346835898
Change-Id: I31be2c8a2057c8a78690454c0d9fd5c152da3db1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5775902


Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1339996}