Implement parameter inheriting

[christopherswenson]

I'm not 100% sure about this behavior yet, so adding the DO NOT MERGE label, and this implementation also feels a bit icky in a way I can't put my finger on yet.

Allows a source to be defined in a way that inherits a parameter from the extended source:

source: state_facts(
  state_filter::string is "CA"
) is duckdb.table('malloytest.state_facts') extend {
  where: state = state_filter
}

// inherits the default value 'CA' from `state_facts`
source: state_facts_ext(state_filter) is state_facts(state_filter)

// should only return one row, `{ state: 'CA' }`
run: state_facts_ext -> { group_by: state }