JVM_IR more aggressive if-null expressions fusion

Assume that changing a return type from T to T?
is not a binary-compatible change.

compiler/testData/codegen/bytecodeText/boxingOptimization/safeCallWithElvisMultipleFiles.kt

@@ -0,0 +1,18 @@
+// MODULE: lib
+// FILE: a.kt
+class A(val x : Int, val y : A?)
+
+// MODULE: main(lib)
+// FILE: main.kt
+fun check(a : A?) : Int {
+    return a?.y?.x ?: (a?.x ?: 3)
+}
+
+// 0 valueOf
+// 0 Value\s\(\)
+
+// JVM_TEMPLATES:
+// 0 ACONST_NULL
+
+// JVM_IR_TEMPLATES:
+// 1 ACONST_NULL