inspect: Support IPv6 addresses in remote address validation

The validateLocation() function in chrome://inspect only accepted
hostnames matching [a-zA-Z0-9\.\-_]+ in the host:port pair,
silently rejecting IPv6 addresses in bracket notation (e.g.
[2001:db8::1]:9222) without any error message.

The C++ backend (HostPortPair::FromString() and the host resolver)
already handles IPv6 literals correctly -- the issue was purely in
the JS UI validation.

Update the regex to also accept bracket-enclosed IPv6 addresses per
RFC 3986, using non-capturing groups for the host part since only the
port (match[1]) is needed.

Bug: 502249088
Change-Id: I38dd90d6220917e4abb9e514e405a5a7963347dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7789272
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1629226}