[4/4] Introduce the kabi tool from Oracle and custom enhancements + documentation.

[casasnovas]

This pull-request adds a new tool, kabi, imported from the Oracle UEK sources. Modifications are
made to it to add an interactive interface augmented with many information required when handling
kABI changes, most notably:

• The list of our maintained binary drivers impacted by the kABI change
• The list of exported symbols modified by a particular type change
• The output of pahole for the original/rebased type
• The list of guilty commits leading to the type change

This PR includes extensive and almost exhaustive documentation on how to neutralize kABI changes.

This pull-request is the last in a series adding tools and documentation on maintaining
our dom0 kernel - for extra context, the final state can be seen here (the final README
especially):

https://github.com/xcp-ng/hypervisor-dev/tree/quentin-main

I've tried to split the changes into palatable/reviewable PRs, full list:

• [1/4] Add script and documentation to generate and refresh a symbol locked list. #2
• [2/4] Introduce the git-review-rebase tool as well as documentation on rebasing to latest upstream. #3
• [3/4] Add chapter on merging back changes from XenServer patch-queue. #4