D3639: remotenames: add paths argument to remotenames revset

[Yuya Nishihara]

> + at revsetpredicate('remotenames([path, ...])')

My proposal was `remotenames([pattern])`, just like bookmark(), tag(),
branch(), etc. If we want a convenient way to specify path prefix, we can
add it to the stringmatcher (e.g. 'remotenames("path:server2")'.) And
multiple paths can be specified as 'remotenames(x) + remotenames(y)', though
it isn't exactly the same as 'remotenames("re:<x>|<y>")'.

Does it make sense?