Type checker shoud unescape field names in projections

[PaulKlint]

Here is an example from lang/rascal/tests/basic/Tuples.rsc that I recently added:

alias TUP = tuple[int \n, str \type];
test bool escape6() {  list[TUP] L = [<1, "a">, <2, "b">]; return L<\n> == [1, 2]; }

gives: "Field \\n does not exist". Using L<n> instead works fine.

Conclusion: the type checker shoud unescape field names in projections.

Note: L.\n works fine.