identify: build the tag list directly instead of using wctx.tags()
The current implementation of workingctx.tags() returns the tags of the parents.
This causes the calculation of {lastesttagdistance} from wdir() to be wrong.
The value when updated to a tag is 0, but updated to the tag's child is 2, the
child of that 3, and so on. This prepares for workingctx.tags() to not report
the parent tags.
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1