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/eqNullableToPrimitiveWithSideEffects.kt

@@ -0,0 +1,19 @@
+// IGNORE_BACKEND: JS, JS_IR, WASM, NATIVE
+var result = ""
+
+fun sideEffecting(): Int {
+    result += "OK"
+    return 123
+}
+
+class C(val x: Int)
+
+val a: C? = C(123)
+val b: C? = null
+
+fun box(): String {
+    if (a?.x != sideEffecting()) return "fail cmp 1"
+    // RHS not evaluated because `b` is null, might be a bug:
+    if (b?.x == sideEffecting()) return "fail cmp 2"
+    return result
+}