Provide equals/hashCode/toString for KParameter implementation

Two KParameter instances are equal iff their backing descriptors are equal and
their callables are equal

compiler/testData/codegen/boxWithStdlib/reflection/methodsFromAny/parametersEqualsHashCode.kt

@@ -0,0 +1,26 @@
+import kotlin.test.*
+
+class A {
+    fun foo(s: String, x: Int) {}
+    fun bar(x: Int) {}
+    val baz = 42
+}
+
+fun box(): String {
+    // Dispatch receiver parameters of different callables are not equal
+    assertNotEquals(A::foo.parameters[0], A::bar.parameters[0])
+    assertNotEquals(A::foo.parameters[0], A::baz.parameters[0])
+
+    assertNotEquals(A::foo.parameters[1], A::bar.parameters[1])
+    assertNotEquals(A::foo.parameters[1], A::foo.parameters[2])
+    assertNotEquals(A::bar.parameters[1], A::foo.parameters[2])
+
+    assertEquals(A::foo.parameters[0], A::foo.parameters[0])
+    assertEquals(A::foo.parameters[0].hashCode(), A::foo.parameters[0].hashCode())
+    assertEquals(A::foo.parameters[1], A::foo.parameters[1])
+    assertEquals(A::foo.parameters[1].hashCode(), A::foo.parameters[1].hashCode())
+    assertEquals(A::bar.parameters[0], A::bar.parameters[0])
+    assertEquals(A::bar.parameters[0].hashCode(), A::bar.parameters[0].hashCode())
+
+    return "OK"
+}

compiler/testData/codegen/boxWithStdlib/reflection/methodsFromAny/parametersToString.kt

@@ -0,0 +1,28 @@
+import kotlin.test.*
+
+fun Int.foo(s: String) {}
+
+class A {
+    fun bar() {}
+}
+
+fun baz(name: String) {}
+
+fun box(): String {
+    assertEquals(
+            listOf("extension receiver of ${Int::foo}", "parameter #1 s of ${Int::foo}"),
+            Int::foo.parameters.map(Any::toString)
+    )
+
+    assertEquals(
+            listOf("instance of ${A::bar}"),
+            A::bar.parameters.map(Any::toString)
+    )
+
+    assertEquals(
+            listOf("parameter #0 name of ${::baz}"),
+            ::baz.parameters.map(Any::toString)
+    )
+
+    return "OK"
+}