Redeclaration of common keyword fields in ADTs as non-common keyword fields

[sungshik]

Describe the bug

There are inconsistencies in how the typechecker and interpreter handle redeclaration of common keyword fields in ADTs as non-common keyword fields.

To Reproduce

Typechecker:

data Foo = foo(int x = 1, int x = 5);  // Error: "Double declaration of field `x`"
data Bar(int x = 1) = bar(int x = 5);  // No error
data Baz(int x = 1) = baz(str x = ""); // No error

Interpreter:

rascal>data Foo = foo(int x = 1, int x = 5);
ok
rascal>foo().x
int: 5
rascal>data Bar(int x = 1) = bar(int x = 5);
ok
rascal>bar().x
int: 1
rascal>data Baz(int x = 1) = baz(str x = "");
io.usethesource.vallang.exceptions.RedeclaredKeywordParameterException: Keyword parameter x was declared earlier as int

Expected behavior

In general, after discussing it with @DavyLandman and @rodinaarssen, I would expect the following rules:

1. Redeclaring a non-common keyword field as a non-common keyword field is forbidden.
2. Redeclaring a common keyword field as a non-common keyword field with the same type is allowed (to change the default).
3. Redeclaring a common keyword field as a non-common keyword field with a different type is forbidden.

Applied to the examples above:

• The compiler and interpreter should report errors for Foo. The interpreter doesn't do this yet.
• The compiler and interpreter should not report errors for Bar, and the defalut should be 5. The interpreter doesn't do this yet.
• The compiler and interpreter should report errors for Baz. The typechecker doesn't do this yet.

[sungshik]

Hi @jurgenvinju, what do you think about this?