Merge from origin/emacs-27

59e768d64a Fix undefined behavior in json.c (Bug#42113)
cce00bef03 Fix ACTION argument of 'display-buffer' call in gud.el
0121db2702 * src/keyboard.c (Fclear_this_command_keys): Doc fix.
b9abf5ceb2 Improve do string of 'man'
b87fc938a0 ; * src/xdisp.c (pos_visible_p): Yet another minor fix for...

diff --cc lisp/man.el
Simple merge

diff --cc lisp/progmodes/gud.el
Simple merge

diff --cc src/json.c
Simple merge

diff --cc src/keyboard.c
Simple merge

diff --cc src/xdisp.c
Simple merge