Antlr produces a warning for token rules that match the same string literal, but not for u/l cased defs

[kaby76]

Antlr produces a warning for this:

FOO1: 'foo';
FOO2: 'foo';

But, it does not produce an error for this:

FOO1: [f] [o] [o];
FOO2: [f] [o] [o];

Antlrvsix should have:

1. The inverse of ulliteral (either send to uppercase string literal or lowercase literal).
2. An analysis to check for this condition and give a warning.

Right now there is nothing in Antlrvsix v8.1.