Support KClass.constructors in reflection

compiler/testData/codegen/boxWithStdlib/reflection/constructors/classesWithoutConstructors.kt

@@ -0,0 +1,19 @@
+import kotlin.reflect.*
+import kotlin.test.assertTrue
+
+interface Interface
+annotation class Anno(val x: Int)
+object Obj
+
+class C {
+    companion object
+}
+
+fun box(): String {
+    assertTrue(Interface::class.constructors.isEmpty())
+    assertTrue(Anno::class.constructors.isEmpty())
+    assertTrue(Obj::class.constructors.isEmpty())
+    assertTrue(C.Companion::class.constructors.isEmpty())
+
+    return "OK"
+}

compiler/testData/codegen/boxWithStdlib/reflection/constructors/simpleGetConstructors.kt

@@ -0,0 +1,29 @@
+import java.util.Collections
+import kotlin.reflect.*
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+open class A private constructor(x: Int) {
+    public constructor(s: String): this(s.length())
+    constructor(): this("")
+}
+
+class B : A("")
+
+class C {
+    class Nested
+    inner class Inner
+}
+
+fun box(): String {
+    assertEquals(3, A::class.constructors.size())
+    assertEquals(1, B::class.constructors.size())
+
+    assertTrue(Collections.disjoint(A::class.members, A::class.constructors))
+    assertTrue(Collections.disjoint(B::class.members, B::class.constructors))
+
+    assertEquals(1, C.Nested::class.constructors.size())
+    assertEquals(1, C.Inner::class.constructors.size())
+
+    return "OK"
+}