rewrites the API docs of favicon_link_tag [ci skip]

Motivated by #14907.
the use of ... in place >> using ... instead

[ci skip]
Merge pull request #14909 from jonatack/patch-7

the use of ... in place >> using ... instead
split nil / Hash cases in url_for

this reduces the number of comparisons and method calls `url_for`
requires.  The nil case no longer calls `symbolize_keys`, we already
know options is nil, so no more ||=, and since it is nil we already know
that options[:host] will be nil too.