Fix VerifyError on primitive override properties

Don't just blindly map property type in PropertyCodegen when generating getter:
we already have its full signature, so we can just as well take the type from
it. The former also isn't correct for properties which are overrides with a
primitive type. Simple mapType is safe for setter though, because the type of a
method parameter cannot change with override on JVM

The change in StackValue relates to call sites of properties which return Unit:
in that case StackValue's this.type is V, whereas the return type of its getter
is Ljet/Unit; -- so coerceTo was coercing from the wrong type in case of getter
calls

 #KT-4373 Fixed
 #KT-4383 Fixed

compiler/testData/codegen/box/properties/kt4383.kt

@@ -0,0 +1,16 @@
+class D {
+    fun get(a: Any, p: PropertyMetadata) { }
+}
+
+object P {
+    val u = Unit.VALUE
+    val v by D()
+    var w = Unit.VALUE
+}
+
+fun box(): String {
+    if (P.u != P.v) return "Fail uv"
+    P.w = Unit.VALUE
+    if (P.w != P.u) return "Fail w"
+    return "OK"
+}