Give names to Unicode code points in C code

Give names to Unicode code points in C code

* src/character.h (NO_BREAK_SPACE, SOFT_HYPHEN)
(ZERO_WIDTH_NON_JOINER, ZERO_WIDTH_JOINER, HYPHEN)
(NON_BREAKING_HYPHEN, LEFT_SINGLE_QUOTATION_MARK)
(RIGHT_SINGLE_QUOTATION_MARK, PARAGRAPH_SEPARATOR)
(LEFT_POINTING_ANGLE_BRACKET, RIGHT_POINTING_ANGLE_BRACKET)
(LEFT_ANGLE_BRACKET, RIGHT_ANGLE_BRACKET)
(OBJECT_REPLACEMENT_CHARACTER):
New named constants for Unicode code points.
* src/bidi.c (bidi_fetch_char, CANONICAL_EQU):
* src/composite.c (char_composable_p):
* src/lread.c (readevalloop, read1):
* src/xdisp.c (get_next_display_element):
Use them.
* src/doc.c (LEFT_SINGLE_QUOTATION_POINT):
Remove; now in character.h.