Support typed literals in expressions

[beikov]

We need some kind of syntax support for some literal types in expressions. EclipseLink defines the following literal inlining syntax: https://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Querying/JPQL#Literals

Hibernate has basically the same but also defines literals for BigDecimal and BigInteger. I think we should also define the literal syntax in our grammar. Right now can't really make any use of these, but when the parser starts to analyze the expressions too, we are going to need the type.

[beikov]

Fixed by 4721e22