grep: add option for logcmdutil.makewalker() to not filter revs by file pats This is needed to implement "grep --all-files".

rust-parsers: use in-place mutation instead of allocating a new `Vec` This is not done for the `dirstate-tree` feature, since it lacks `iter_mut`. Differential Revision: https://phab.mercurial-scm.org/D9136

revlog: pre-compute null revlog item for pure version The dynamically created tuple shows up in memory profiles and the use of nullid prevents the normal constant building to work. Differential Revision: https://phab.mercurial-scm.org/D9154