This allows using <Esc> <Esc> <letter> in a macro as an alternative
for <Ctrl+letter>, but it does require that one does not type <Esc>
by accident when recording a macro as it might modify the subsequent
keystroke when the macro is replayed.
This fixes https://savannah.gnu.org/bugs/?58904.
Bug existed since version 3.0, commit ecc9211a.