bug#53214: Release 1.4.0 progress

[Ludovic Courtès]

Hello!

This pseudo-bug is here to keep track of bug fixes and patch series we
aim to address for 1.4.0.

To add an issue as “required” for 1.4.0, mark this bug as “blocked” by
this issue (this is ‘C block NUMBER RET’ in debbugs.el).

Ludo’.