Bug 1813618 - buffer client auth certificate selection UI for speculative...

Bug 1813618 - buffer client auth certificate selection UI for speculative connections r=valentin,jschanck,necko-reviewers,kershaw

When necko makes a speculative connection, the peer may ask for a client
authentication certificate. This patch makes it so that when this happens,
no certificate selection UI will be shown until the connection is claimed (as
in, it is no longer merely speculative).

Differential Revision: https://phabricator.services.mozilla.com/D175528