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

tests/misc_testsuite/simd/replace-lane-preserve.wast

@@ -0,0 +1,12 @@
+;; originally from #3216
+(module
+  (func (result i64)
+    v128.const i64x2 -1 1
+    global.get 0
+    f64x2.replace_lane 0
+    i64x2.extract_lane 1
+  )
+  (global f64 (f64.const 1))
+  (export "" (func 0)))
+
+(assert_return (invoke "") (i64.const 1))