[JavaScript / Python] Make a pass to implement missing pre-defined Date format

### Description

It was reported here that "R" format is not supported by Fable, and I suspect some other format are missing too.

https://github.com/microsoft/referencesource/blob/51cf7850defa8a17d815b4700b67116e3fa283c2/mscorlib/system/globalization/datetimeformat.cs#L99-L124

### Related information

* Fable version: `4.24.0`
* Operating system
