dirstate: add a `update_file` function...
dirstate: add a `update_file` function
This function is the other side of the `set_tracked`/`set_untracked` API revamp.
It is to be used when the dirstate is changing its parents during and update or
a merge. It states all the information we know about the file so that the
dirstate can update its internal data.
Unlike the `set_tracked`/`set_untracked` it has not regards for the information
previously tracked in the tristate.
Differential Revision:
https://phab.mercurial-scm.org/D11075
