Only recognize URIs with balanced parentheses

To prevent URIs inside parentheses from getting extended to the closing
parenthesis, only recognize URIs with balanced parentheses in regname,
path, query and/or fragment.  We still allow unbalanced parenthesis in
userInfo, since the postfix @ should prevent most ambiguous situations,
and the parenthesis can be part of a password.

CCBUG: 455166