Add relaxed_trunc_f32x4_s, relaxed_trunc_f32x4_u, relaxed_trunc_f64x2_s_zero, and relaxed_trunc_f64x2_u_zero
<rdar://problem/110554488>
Pull request: https://github.com/WebKit/WebKit/pull/14875
Committed 265136@main (46168caf6713): <https://commits.webkit.org/265136@main> Reviewed commits have been landed. Closing PR #14875 and removing active labels.