icu4c api proposal: add U_IS_SUPPLEMENTARY(c) and U_IS_BMP(c)

Jitterbug 2913 says it all, quote:

Some users are confused between surrogates and supplementary code points. There
is a macro U_IS_SURROGATE(c), but users indicate that it would help avoid some
confusion if there were macros U_IS_SUPPLEMENTARY(c) and U_IS_BMP(c) as well.

In short, a surrogate is a pseudo-character with a value D800..DFFF, and a
matched pair of two surrogates in UTF-16 encodes a supplemenary code point,
which in turn has a code point value of 10000..10FFFF.

add to utf.h:
#define U_IS_SUPPLEMENTARY(c) ((c)>0xffff)
#define U_IS_BMP(c) ((uint32_t)(c)<=0xffff)


Expiration: Friday, 2003-nov-07

Sincerely,
markus