tags-cache: add a dedicated warm cache function to hgtagsfnodescache Having a dedicated API point will help to optimize that specific usage. Right doing a full phases weam takes a long time, even when the cache is already filled.

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    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "phabricator.uri": "https://phab.mercurial-scm.org/",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
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