Don't show argument name hints for dynamic calls.

Mark function descriptors created for dynamic calls as having
synthesized parameter names.

 #KT-21275 Fixed

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tasks/dynamicCalls.kt

@@ -136,6 +136,7 @@ class DynamicCallableDescriptors(storageManager: StorageManager, builtIns: Kotli
                 Modality.FINAL,
                 Visibilities.PUBLIC
         )
+        functionDescriptor.setHasSynthesizedParameterNames(true)
         return functionDescriptor
     }
 

idea/tests/org/jetbrains/kotlin/idea/parameterInfo/InlayParameterHintsTest.kt

@@ -172,4 +172,10 @@ annotation class ManyArgs(val name: String, val surname: String)
             fun <T> T.test(block: (receiver: T, Int) -> Unit) = block(<hint text="receiver:"/>this, 0)
         """)
     }
+
+    fun `test dynamic`() {
+        check("""fun foo(x: dynamic) {
+            x.foo("123")
+        }""")
+    }
 }