bug#36454: 26.2.90; feature request - Insert char by hex tab completion or C-x 8 RET ffe <TAB>

[Sebastian Urban]

> A good place to end.

Before that, what about (additional) variable which would control
completion style in this case, with values:
- name - default, completion in 'insert-char' would work like it works
  now,
- name-and-hex - completion in 'insert-char' would also complete hex
  codes and show everything in *Completions* window,

or just t/nil instead of name/name-and-hex.