Add functionality for checking validity of names

This replicates in the Haskell Query2 implementation the behaviour of
the Python code: if a "simple" filter is passed (one that contains
only Or aggregators  and EQ binary ops on the name field), then an
failure is flagged if the given values are not known.

Our implementation is pretty straightforward, with a few details:

- we ignore any NumericValues passed, since that inconsistency will be
  flagged by the filter compiler
- we return an the non-normalized names from the getRequestedNames
  function, and not the fully-normalized ones; this will be done later
  in individual query functions
- we test a few of the desired behaviours of the above-mentioned
  function

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Agata Murawska <agatamurawska@google.com>