Document cond_copysign and cond_len_copysign optabs [PR112951]

Document cond_copysign and cond_len_copysign optabs [PR112951]

This adds the documentation for cond_copysign and cond_len_copysign optabs.
Also reorders the optabs.def to be in the similar order as how the internal
function was done.

gcc/ChangeLog:

	PR middle-end/112951
	* doc/md.texi (cond_copysign): Document.
	(cond_len_copysign): Likewise.
	* optabs.def: Reorder cond_copysign to be before
	cond_fmin. Likewise for cond_len_copysign.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>