Summary:
Added NumberParse.ts, counterpart of NumberFormat.ts.
Contains generic functionality for parsing numbers formatted by Intl.NumberFormat, not tied to documents or anything.
This doesn't change any actual behaviour, applying this parsing when pasting/typing in numeric columns will be a separate diff.
Test Plan: New file with extensive unit tests.
Reviewers: dsagal
Reviewed By: dsagal
Subscribers: jarek
Differential Revision: https://phab.getgrist.com/D3078
