dirstate: add a function to update tracking status while "moving" parents The `scmutil.dirstateparent` is moving the dirstate parent without touching the working copy. It is used by history-rewriting operations like amending of folding. The function was directly doing the "low level" computation and dirstate change. All that logic belong to the dirstate and should be moved there. For this purpose we introduce a new function that does just that and use it. Differential Revision: https://phab.mercurial-scm.org/D11012

dirstate: introduce an internal `_drop` method We want to split current user of `dirstate.drop` between `hg rm`-like cases and update of the dirstate coming from update/merge. To do this we will introduce new API. The first step is to introduces an internal function that these new API migh use (or not use) to distinct between the migrated users and the others. Differential Revision: https://phab.mercurial-scm.org/D11023

dirstate: introduce an internal `_remove` method We want to split current user of `dirstate.remove` between `hg rm`-like cases and update of the dirstate coming from update/merge. To do this we will introduce new API. The first step is to introduces an internal function that these new API migh use (or not use) to distinct between the migrated users and the others. Differential Revision: https://phab.mercurial-scm.org/D11011