desktop: Simplify the parsing logic
* read-desktop.h (desktop_reader_class_ty): Rename 'handle_text'
to 'handle_blank'.
(desktop_reader_handle_blank): Rename from
'desktop_reader_handle_text'.
* read-desktop.c (SIZEOF): New macro.
(desktop_reader_handle_blank): Rename from
'desktop_reader_handle_blank'.
(read_until_newline, read_group_name, read_key_name): Remove.
Merge into...
(desktop_lex): ...here.
(desktop_parse): Call 'desktop_lex' instead of read_*. Don't
normalize whitespaces.
(enum token_type_ty): New enum.
(struct token_ty): New struct.
(free_token): New function.
* write-desktop.c (msgfmt_desktop_handle_blank): Rename from
'msgfmt_desktop_handle_text'.
* x-desktop.c: Include "c-ctype.h".
(extract_desktop_handle_comment): Normalize whitespaces here.
(extract_desktop_handle_blank): Rename from
'extract_desktop_handle_text'.
