Fix treesit-query-capture

Fix treesit-query-capture

Before this change Ftreesit_query_capture doesn't convert character
position to byte position for BEG and END parameters.  I observed
fontification issue in css files but couldn't figure out why, now I
know :-)

I decide to keep treesit--font-lock-query-expand-range, since it might
provide a escape hatch for problems we discover in the future, and it
should be very cheap so no downside of keeping it.

* lisp/textmodes/css-mode.el (css-ts-mode): Stop setting
treesit--font-lock-query-expand-range.
* lisp/treesit.el (treesit--font-lock-query-expand-range): Update
docstring.
* src/treesit.c (Ftreesit_query_capture): Convert BEG and END to byte
position.  Also added parentheses wround "beg_byte - visible_beg" in
the call to ts_query_cursor_set_byte_range (i.e., style change).