Add additional Intl.NumberFormat grouping options

[sffc]

Currently, useGrouping is a boolean. However, CLDR and ICU provide mechanisms for more fine-grained control over grouping sizes. ICU provides five options for the grouping strategy.

We could extend useGrouping with string-based options to support these additional modes.

Additional context: https://bugs.chromium.org/p/chromium/issues/detail?id=989442

[sffc]

I plan to address this as part of my new proposal Intl.NumberFormat V3.

https://github.com/sffc/proposal-intl-numberformat-v3

[sffc]

Please move further discussion to the new proposal repo, e.g.:

tc39/proposal-intl-numberformat-v3#3

[sffc]

This is landed in Intl.NumberFormat v3.