Update with stellar-xdr with split interface version

[leighmcculloch]

What

Update with stellar-xdr with split interface version.

Why

See:

• https://github.com/stellar/stellar-xdr/pull/212

Dependent on:

• https://github.com/stellar/stellar-xdr/pull/212
• https://github.com/stellar/stellar-xdr/pull/213
• https://github.com/stellar/rs-stellar-xdr/pull/389