Add a test that mkMethod call causes a type error. (#12175)

Relevant discussion: https://github.com/digital-asset/daml/pull/12171#discussion_r770553009

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compiler/damlc/tests/daml-test-files/MkMethodTypeError.daml

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+-- Copyright (c) 2021 Digital Asset (Switzerland) GmbH and/or its affiliates. All rights reserved.
+-- SPDX-License-Identifier: Apache-2.0
+
+-- @SINCE-LF-FEATURE DAML_INTERFACE
+-- @ERROR error type checking value MkMethodTypeError.main: unknown data type
+
+-- | Verify that calling mkMethod outside of desugared interface method definitions is an LF type error.
+module MkMethodTypeError where
+
+data T = T
+
+instance HasInterfaceTypeRep T where interfaceTypeRep = undefined
+instance HasToInterface T T where _toInterface x = x
+instance HasFromInterface T T where fromInterface = Some
+instance DA.Internal.Desugar.HasMethod T "foo" T where
+
+main : Int
+main =
+    let _ = DA.Internal.Desugar.mkMethod @T @T @"foo" identity
+    in 10