Do not apply constant folding for non built-in functions

#KT-15872 Fixed

compiler/testData/codegen/box/operatorConventions/infixFunctionOverBuiltinMember.kt

@@ -0,0 +1,18 @@
+infix fun Int.rem(other: Int) = 10
+infix operator fun Int.minus(other: Int): Int = 20
+
+fun box(): String {
+    val a = 5 rem 2
+    if (a != 10) return "fail 1"
+
+    val b = 5 minus 3
+    if (b != 20) return "fail 2"
+
+    val a1 = 5.rem(2)
+    if (a1 != 1) return "fail 3"
+
+    val b2 = 5.minus(3)
+    if (b2 != 2) return "fail 4"
+
+    return "OK"
+}

compiler/testData/codegen/light-analysis/operatorConventions/infixFunctionOverBuiltinMember.txt

@@ -0,0 +1,6 @@
+@kotlin.Metadata
+public final class InfixFunctionOverBuiltinMemberKt {
+    public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
+    public final static method minus(p0: int, p1: int): int
+    public final static method rem(p0: int, p1: int): int
+}