Foward-port CHANGELOG entries from 9.x, 10.x, 11.x, 12.x

[apoelstra]

See github/advisory-database#4719

Right now to see the CHANGELOG for versions that have backported fixes, you need to dig through the git history or download specific versions from crates.io. All the information should exist in CHANGELOG.md on master.

[benma]

Currently the CHANGELOG entry for 12.3.1 seems to be completely missing, and the one for 12.3.0 can be found at the tag but not in master (currently: https://github.com/rust-bitcoin/rust-miniscript/blob/e33e66c3e4540fd1af3e322370e4d8f69a8cfc59/CHANGELOG.md).