HPCC-10549 Use graph results for spilled wu results

This pull request contains a few related changes
- A new function for accesing a single row result.  It improves the
  generated code a bit (not as much as I hoped).
- Better serializitation of fields inside onStart - reduces code.
- Options to generate graph results for all spills, or just those spills
  that will be accessed from a child query
- Implement resolveLocalQuery(0) in hthor and roxie
- Add a way of conditionally including a compound statement (e.g,m a function
  definition) if other - non boilerplate code - was added.
- Add a way of conditionally generating code if another statement is included.
- Flag which graph results are used from child queries

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>