[V1] Remove PartiQLValue from the AST

[RCHowell]

Some AST cleanup work,

• The AST should have its own representation of values independent of PartiQLValue (to be deprecated) and Datum.
• Similarly, the AST should not necessarily be dependent on partiql-types/partiql-spi packages (but ok if more practical).

To the first point, notice how AST types are independent of PType as there are many syntaxes for a single type e.g. BOOL|BOOLEAN.

This PR would require defining AST expr literal variants for the parser rules

literal
    : NULL                                                                                # LiteralNull
    | MISSING                                                                             # LiteralMissing
    | TRUE                                                                                # LiteralTrue
    | FALSE                                                                               # LiteralFalse
    | LITERAL_STRING                                                                      # LiteralString
    | LITERAL_INTEGER                                                                     # LiteralInteger
    | LITERAL_DECIMAL                                                                     # LiteralDecimal
    | ION_CLOSURE                                                                         # LiteralIon
    | DATE LITERAL_STRING                                                                 # LiteralDate
    | TIME ( PAREN_LEFT LITERAL_INTEGER PAREN_RIGHT )? (WITH TIME ZONE)? LITERAL_STRING   # LiteralTime
    | TIMESTAMP ( PAREN_LEFT LITERAL_INTEGER PAREN_RIGHT )? (WITH TIME ZONE)? LITERAL_STRING   # LiteralTimestamp
    ;

Along with updating the pretty-printer in org.partiql.ast.sql