[libc][math] Reorganize sinf and cosf function selection (#226529)

Reorganises sinf and cosf similarly to #224735 such that:
src/__support/math/func.h selects implementation, and
src/__support/math/func_<type>_eval.h implements func with <type> as the
intermediate computational type.

GitOrigin-RevId: 09cdef016cfc756b29002cd7870c63b7f1b09c6b