obsolete: unify collapsed revisions markers handling When collapsing A, B and C into D, amend was registering: A -> D B -> D A -> B C -> D A -> C while the rebase wrapper was doing: A -> D B -> D C -> D At this point, I have no argument to favor one or another or even a new one like: A -> B B -> C C -> D so I am aligning the rebase implementation on the older amend one. At least we can now change them all at once.

rebase: improve invalid revisions filtering - Filter rebasestate nullmerge and unrebased revision before considering updating obsolete. This simplifies the handling of obsolete and make it ignore unrebased revision rather than extinguishing them. - Apply obsolete markers only if rebasestate is not empty, testing rebasetarget was irrelevant.