repoview: add a new filtername for accessing hidden commits This patch adds a new filter 'visible-hidden' for repository and will be used to return a repo object with user passed revisions unhidden. Unlike the directaccess extension in fb-hgext and previous series adding the functionality, this time we introduce only one new filter as whether to warn user or not is handled by scmutil.unhidehashlikerevs(). Differential Revision: https://phab.mercurial-scm.org/D1734