Move range_tree, btree, highbit64 to common code

[tonyhutter]

Motivation and Context

Break out range_tree/btree/highbit64/lowbit64 code for #17864

Description

Break out the range_tree, btree, and highbit64/lowbit64 code from kernel space into shared kernel and userspace code. This is needed for the updated zpool status -vv error byte range reporting that will be coming in a future commit. That commit needs the range_tree code in kernel and userspace.

How Has This Been Tested?

Test built

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[tonyhutter]

Note - I kept highbit64() and lowbit64() as inline functions rather than macros, since some parts of our code expected them to return an int specifically.

[tonyhutter]

I think this is ready for review

[robn]

Works for me!

(incidentally, I've a bunch of stuff in-flight around linkages, symbol visibility, common code, etc, so I will likely end up shuffling this a bit along with a ton of other stuff when I get back to it. Nothing here changes anything for me there, and hopefully next time this sort of thing will be a lot easier).