Move insertlane to ISLE (#3544)

This also fixes a bug where `movsd` was incorrectly used with a memory
operand for `insertlane`, causing it to actually zero the upper bits
instead of preserving them.

Note that the insertlane logic still exists in `lower.rs` because it's
used as a helper for a few other instruction lowerings which aren't
migrated to ISLE yet. This commit also adds a helper in ISLE itself for
those other lowerings to use when they get implemented.

Closes #3216

cranelift/codegen/src/isa/x64/lower/isle.rs

@@ -207,6 +207,13 @@ where
             None
         }
     }
+
+    #[inline]
+    fn sse_insertps_lane_imm(&mut self, lane: u8) -> u8 {
+        // Insert 32-bits from replacement (at index 00, bits 7:8) to vector (lane
+        // shifted into bits 5:6).
+        0b00_00_00_00 | lane << 4
+    }
 }
 
 #[inline]