* bidi.c (bidi_fetch_char): Swap first and second arguments

* bidi.c (bidi_fetch_char): Swap first and second arguments
to match other functions accepting character and byte positions.
Adjust comment.
(bidi_resolve_explicit_1, bidi_level_of_next_char): Adjust users.
(bidi_paragraph_init): Likewise.  Use DEC_BOTH which is faster
when you need just to move to the previous buffer position.
* xdisp.c (Fcurrent_bidi_paragraph_direction): Use DEC_BOTH.