Flatten the getEvents response schema

[Shaptic]

What problem does your feature solve?

The current schema for the event value does not make sense: according to the getEvents documentation, we have

{
  // ...other fields...
  value: {
    xdr: string
  }
}

where xdr is a serialized ScVal. This nested structure offers no add'l value.

What would you like to see?

A flatter structure:

{
  value: string;
}

It would be highly beneficial to get this in prior to a stable build due to the fact that it's a breaking change.

What alternatives are there?

This can be abstracted client-side, but it's cleaner if it comes from the server.

[sydneynotthecity]

Confirm if this will be a breaking change for SDKs and whether we are willing to refactor in downstream clients.

[Shaptic]

This would be a breaking change, yes, but I imagine it would be quite a small + painless one for most SDKs (i.e. mostly just a schema change).

Similarly, SDK consumers would just need to change all calls from .value.xdr to .value, which doesn't seem like a lot of lift to expect in a release candidate given a cleaner API.