absorb: graduate -i flag from experimental

The interactive mode seems to work well. I have previously thought
that `-i` should be what `-e` does, but the current behavior matches
what other `-i` flags do (select a subset of the hunks), so I think
that is what we want.

Differential Revision: https://phab.mercurial-scm.org/D8055

hgext/absorb.py

@@ -1077,7 +1077,7 b' def absorb(ui, repo, stack=None, targetc'
             b'i',
             b'interactive',
             None,
-            _(b'interactively select which chunks to apply (EXPERIMENTAL)'),
+            _(b'interactively select which chunks to apply'),
         ),
         (
             b'e',