EXEC allows any token on RHS

[johnedquinn]

Description

SqlParser allows ANY token on RHS of Exec. We need to eventually formalize what EXEC should handle on RHS. Likely literal strings, identifiers (quoted and unquoted).

To Replicate

To replicate:

PartiQL> EXEC a
!!
PartiQL> EXEC $
!!
PartiQL> EXEC %
!!
PartiQL> EXEC *
!!
PartiQL> EXEC =
!!

More Information

I'm leaving a TODO in PartiQLParser (experimental) to address this. Since we currently allow any type of token, I will specifically allow expressions that evaluate to strings and identifiers -- since I know we shouldn't be allowing any token.

[johnedquinn]

Resolved by #711