C# HTTP handlers - Module Bindings

[JasonAtClockwork]

Description of Changes

Adding C# HTTP handlers based on #4636

• adds the C# handler/router API [SpacetimeDB.HttpHandler], [SpacetimeDB.HttpRouter]
• wires C# HTTP handlers into module definition/build/runtime registration
• mirrors the Rust/TypeScript HTTP smoketests and adds C# docs coverage
• updates the HTTP handlers docs with C# examples
• refactored ProcedureContext to allow for a central location for WithTx/TryWithTx to support HandlerContext
• routes use a generated Handlers.* tokens to avoid raw strings

API and ABI breaking changes

Adds new APIs for the HTTP handler and should not be breaking

Expected complexity level and risk

3 - this hit the binding, module registration, and had a decent refactor for ProcedureContext

Testing

• Expanded crates/smoketests/tests/smoketests/http_routes.rs with C# mirrors of the Rust HTTP
  route tests

I also did some manual testing with a throw away project, and will be adding to the module-test after all languages are caught up on HTTP handlers.