Optimize PropertyMetadataImpl instance creation

Create all property metadatas in <clinit> and save them to a static array
$propertyMetadata. Getter/setter of each delegated property will then just
obtain the corresponding instance from that array

 #KT-4232 Fixed

compiler/testData/codegen/box/delegatedProperty/propertyMetadataShouldBeCached.kt

@@ -0,0 +1,46 @@
+import java.util.IdentityHashMap
+
+class A {
+    var foo: Int by IntHandler
+
+    class object {
+        var bar: Any? by AnyHandler
+    }
+}
+
+val baz: String by StringHandler
+
+
+
+val metadatas = IdentityHashMap<PropertyMetadata, Unit>()
+
+fun record(p: PropertyMetadata) = metadatas.put(p, Unit.VALUE)
+
+object IntHandler {
+    fun get(t: Any?, p: PropertyMetadata): Int { record(p); return 42 }
+    fun set(t: Any?, p: PropertyMetadata, value: Int) { record(p) }
+}
+
+object AnyHandler {
+    fun get(t: Any?, p: PropertyMetadata): Any? { record(p); return 3.14 }
+    fun set(t: Any?, p: PropertyMetadata, value: Any?) { record(p) }
+}
+
+object StringHandler {
+    fun get(t: Any?, p: PropertyMetadata): String { record(p); return p.name }
+    fun set(t: Any?, p: PropertyMetadata, value: String) { record(p) }
+}
+
+fun box(): String {
+    val a = A()
+    a.foo = 42
+    a.foo = a.foo + baz.length
+    a.foo = 239
+    A.bar = baz + a.foo
+    baz + A.bar
+
+    if (metadatas.keySet().size() != 3)
+        return "Fail: only three instances of PropertyMetadata should have been created\n${metadatas.keySet()}"
+
+    return "OK"
+}