Implements KAnnotatedElement.hasAnnotation()

This commit fixes KT-29041, by adding a convenience method to verify if a certain `KAnnotatedElement` has an annotation or not

compiler/testData/codegen/box/reflection/annotations/hasAnnotation.kt

@@ -0,0 +1,25 @@
+// TARGET_BACKEND: JVM
+// WITH_REFLECT
+
+import kotlin.reflect.full.hasAnnotation
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+annotation class Baz
+annotation class Far
+
+@Baz
+@Far
+class Foo
+
+class Bar
+
+fun box(): String {
+    assertFalse(Bar::class.hasAnnotation<Baz>())
+    assertFalse(Bar::class.hasAnnotation<Far>())
+
+    assertTrue(Foo::class.hasAnnotation<Baz>())
+    assertTrue(Foo::class.hasAnnotation<Far>())
+
+    return "OK"
+}

core/reflection.jvm/src/kotlin/reflect/full/KAnnotatedElements.kt

@@ -26,3 +26,10 @@ import kotlin.reflect.*
 inline fun <reified T : Annotation> KAnnotatedElement.findAnnotation(): T? =
         @Suppress("UNCHECKED_CAST")
         annotations.firstOrNull { it is T } as T?
+
+/**
+ * Returns true if this element is annotated with [T], false otherwise
+ */
+@SinceKotlin("1.4")
+inline fun <reified T : Annotation> KAnnotatedElement.hasAnnotation(): Boolean =
+        findAnnotation<T>() != null