Legacy support (borsh-js)

[marcus-pousette]

Can this library by compatible with borsh-js schemas in a simple way? Many existing users are depending on borsh-js and do not perhaps want to rewrite everything if it is already working.

The support has to work two way. I.e. There should be a way of getting borsh-js schemas into borsh-ts and borsh-ts into borsh-js schemas.

Issues:

• borsh-js uses 'BN' instead of 'bigint' for u64 and above.
• Enum representation in borsh-ts assumes that one creates a class for each enum type, whereas in borsh-js enums are simply enumerated.
• borsh-ts supports custom serializers which will not work out of the box with borsh-js
• When fixing all these compatibility issue, there will be a lot more (complicated) code, and a lot of test code has to be written (perhaps all of this would be a separate module)