Add a SpacetimeDBException to C# SDK to aid in debugging

[rekhoff]

Description of Changes

This implements a fix to an issue with debugging using the C# SDK, by adding new exception types:

• SpacetimeDBException,
• SpacetimeDBArgumentException,
• SpacetimeDBEmptyReducerNameException

Additional, regenerating bindings will now allow clients to report an SpacetimeDBEmptyReducerNameException rather than an ArgumentOutOfRangeException when the client receives an empty reducer name from the server.

An example of the generated code currently, that results in the exception:

SpacetimeDB/sdks/csharp/examples~/quickstart-chat/client/module_bindings/SpacetimeDBClient.g.cs

Line 475 in 544e2ed

var reducer => throw new ArgumentOutOfRangeException("Reducer", $"Unknown reducer {reducer}")

Note: Normally this is not an issue for a client, because the SpacetimeDBEmptyReducerNameException would be caught by the Try/Catch statement, but a debugger will still catch the exception and halt operation. This can be annoying to a developer when debugging.

By separating out the exception into a custom Exception type, we allow a developer to flag the new exception type as something it can ignore, without ignoring other relevant exceptions.

API and ABI breaking changes

Not a breaking change.
Clients will need to regenerate bindings to get the new exceptions

Expected complexity level and risk

1

Testing

• Tested regenerating bindings and confirmed intended output.
• Tested debugging and receiving SpacetimeDBEmptyReducerNameException when expected.

[github-actions]

Some missing or dangling .meta found. Fix commits are needed.

Status	File
Not committed	src/Exceptions.cs.meta

[jdetter]

Haven't tested this myself but I was involved in the early testing of this PR and also this is quite simple. LGTM 👍