chore(core): rename Uni_IsSMP to Uni_NonBMP

[srl295]

Suggest to rename Uni_IsSMP() to Uni_IsNonBMP() across unicode.h and kmcompx.h as it is misleading. The SMP is exactly U+10000..U+1FFFF only. Only used in a few places.

Discussed this at #10557.

[mcdurdin]

Yes my bad, back in probably 1998. SMP stands for Some More Planes and covers everything that is not in the BMP. Doesn't it?

[mcdurdin]

To be honest, the name is still ambiguous: what data type does it accept? I guess it takes a USV (u)int32_t but... that's different to some of the other Uni_ macros.

The Uni_ class of macros in unicode.h could all be reviewed for better names.