Rename KClass.properties and extensionProperties: prepend 'member'

To better emphasize the fact that all returned properties require an instance
of the class they are declared in. Another issue was that
'Some::class.extensionProperties' was sometimes incorrectly perceived as
"get all extension properties available on the class Some"

compiler/testData/codegen/reflection/classLoaders/differentClassLoaders.kt

@@ -15,8 +15,8 @@ class Test {
         assertNotEquals(k1, k2)
 
         // The same for properties of these classes
-        val p1 = k1.properties.first()
-        val p2 = k2.properties.first()
+        val p1 = k1.memberProperties.first()
+        val p2 = k2.memberProperties.first()
         assertEquals("$p1", "$p2")
         assertNotEquals(p1, p2)
     }