convertbookmark: properly convert stacked bookmarks We ignores pure descendant when looking for revision to convert. This adds support for cases were a linear stack contains multiple bookmark (or un-bookmarked descendants exists). In this case, some changeset are left orphan, but we'll consider the issue as minor for now.

convertbookmark: perform all actions at the end This will make the whole operation more deterministic and robust.

converbookmark: split target computation from actual update This will allow for further refactoring helping consistency.

convertbookmark: extract the revset into a module level constant This will make it easier to read and modify the query.

convertbookmark: properly exclude public changeset Public changeset are immutable and cannot have a topic anyway.

test: add a new root changeset to all debugconvertbookmark test case We'll make this root changeset public to check the debugconvertbookmark logic in that regards. It is added in its own changeset since it massively impact all output.

tests: import section in 'test-topic-debugcb.t' We now have two levels of titles to clarify some aspect of the tests.

test: avoid using debugdrawdag in 'test-topic-debugcb.t' The 'debugdrawdag' utility adds local tags that prevent hidden changeset to get hidden. We will do without that extension for now.

tests: add more tests for debugconvertbookmark

convertbookmark: add logic to skip revisions with multiple bookmarks When a user tries to converts a bookmark to topic which is on a changeset with more bookmarks we skip that.