destupdate: have a generic and extensible way to run each step We want extension to be able to easily override or add new way to select the default update destination. We use the same list + dict approach as in other parts of the code.

destupdate: extract logic based on branch in its own function One of the main goal of having consolidated destination function is to allow extension to play with this logic. We extract sub logic to make is wrapping more practical.

destupdate: extract logic based on bookmarks in its own function One of the main goal of having consolidated destination function is to allow extension to play with this logic. We extract sub logic to make is wrapping more practical.

destupdate: extract logic based on obsolescence marker in its own function One of the main goal of having consolidated destination function is to allow extension to play with this logic. We extract sub logic to make is wrapping more practical.

destupdate: move obsolete handling first This block was overwriting any result from the previous block anyway. So we move it first to prove it is possible and we'll extract it in its own function in the next patch.

destupdate: indent bookmark and branch logic We'll move the obsolete related logic first (as it is overwriting any other anyway) to make the next patch clearer we add indentation in this one.

destupdate: extract validation logic One of the main goal of having consolidated destination function is to allow extension to play with this logic. We extract sub logic to make is wrapping more practical.

rebase: rename and test '_destrebase' We make the name consistent with the other similar revsets and make sure it has minimal tests.

rebase: directly use '_destrebase' There is little value in using the revset instead of the function.

rebase: extra default destination in its own function This makes it much simple to wrap for other extension.