Merge from origin/emacs-27

4b9fbdb5a7 ; Update TODO item about ligature support
03d44acfdd * doc/lispref/control.texi (Processing of Errors): Improve...
b48ab743a8 Minor fixups for mutability doc
6ac2326e5b Don’t use “constant” for values you shouldn’t change

diff --cc doc/lispintro/emacs-lisp-intro.texi
Simple merge

diff --cc doc/lispref/objects.texi
Simple merge