Summary:
Following discussion in https://phab.getgrist.com/D3164:
- Change createParser to accept docData and one or two metadata row IDs and let it extract the metadata, so it's more easily usable in the server.
- Change ViewFieldRec.valueParser observable to a function createValueParser.
Test Plan: Existing tests.
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D3172