(describe-char): Create link buttons for `charset'

(describe-char): Create link buttons for `charset'
and `code point'.  Add the current input method name with a link
button to `to input' field.  Print face names of display table
characters in `The display table entry is displayed by' section
instead of printing face-id in the `display' field.
Guess hardcoded faces and create a link button for them.
Skip empty fields when calculating max-width.
Treat `widget-create' specially while inserting strings from the
collected field list.
(describe-char-after): Made obsolete in version 22.1, not 21.5.