`Identity` and `ConnectionId` should implement `IComparable`

[rekhoff]

Issue:

When attempting to create a table that uses Identity as an index of a BTree like:

#[index(btree)]
pub identity: Identity,

Generated code in C# will throw the error:
The type 'SpacetimeDB.Identity' must be convertible to 'System.IComparable<SpacetimeDB.Identity>' in order to use it as parameter 'Column' in the generic class 'SpacetimeDB.RemoteTableHandle<EventContext,Row>.BTreeIndexBase<Column>'

This is because SpacetimeDB.Identity does not implement the IComparable interface:

SpacetimeDB/crates/bindings-csharp/BSATN.Runtime/Builtins.cs

Line 204 in 7cb509c

public readonly record struct Identity

While we are at it, it makes sense to implement IComparable for ConnectionId as well:

SpacetimeDB/crates/bindings-csharp/BSATN.Runtime/Builtins.cs

Line 121 in 7cb509c

public readonly record struct ConnectionId

[joshua-spacetime]

Note, unique constraints (which should be generating the same btree index) work just fine

#[unique]
pub identity: Identity,

[rekhoff]

Resolved by PR #2354