modified comments pertaining to function arguments to not be reliant on a particular formatting (// to /* */)

fix -Werror=ignored-qualifiers

now you reverted PR19132's changes completely

updated backporting.md

fixing docs

added test cases and removed test cases that no longer apply (the number of digits in PRs are no longer in the code)

making the tests happy

In D9257#210616, @PiRK wrote:

Ok wigh core-gui. But something need to be done about the automatic " PRxxxx to URL" conversion.

yea this ain't worth it

we need to come up with a standard notation to ease automation of tagging the done backports in the bitcoin-core/gui repo, what about using Backport of core-gui PRxxxxxx?

couldn't reproduce with for i in {1..100}; do ninja check-bitcoin-coinselector_tests; done, rebasing

this should probably be the last step once all of cashtab is proper React'd

addressed comments

@bot build-tsan

rebase on top of D9191