JVM_IR: fix primitive comparison optimizations

1. the `primitive == object?.something` fusion should not apply to
    `primitive.equals(object?.something)` because it can't;

 2. coercions to Int are there for a reason - don't remove them;

 3. better optimize `primitive == object?.something` -- the result
    should be subject to if-null fusion, so it needs to have a specific
    pattern that resembles safe calls.

 #KT-47597 Fixed

compiler/testData/codegen/box/binaryOp/eqNullableShortToShort.kt

@@ -0,0 +1,7 @@
+class C(val x: Short)
+
+fun box(): String {
+    val a: C = C(1)
+    val b: C? = C(1)
+    return if (b?.x == a.x) "OK" else "fail"
+}