(x_output_toolbar_button): Use <Charc_dynarr *> instead of

(x_output_toolbar_button): Use <Charc_dynarr *> instead of
<Emchar_dynarr *> for buf; use
`convert_bufbyte_string_into_charc_dynarr' instead of
`convert_bufbyte_string_into_emchar_dynarr'; use
`find_charsets_in_charc_string' instead of
`find_charsets_in_emchar_string'.