Release v4.258.0

Added

• Body-execution providers can now run reaction bodies through ISemanticBodyExecutionProvider.ReactAsync. A reaction with a single event trigger and a standalone body produces events or invokes commands from the body's result, after where. The whole result is validated before anything settles. Without a provider, behaviour is unchanged (part of #1099)
• The new PerformAsync method on ISemanticBodyExecutionProvider defines the provider contract for snapshot query performers. It answers Unsupported by default, and the reference run does not call it yet (part of #1099)