Add IEventLoopControl APIs to hermes-interface

Summary:
Adds `ISetEventLoopControl` to the Hermes-specific JSI. This interface
specifies an user-defined, thread-safe function to schedule some task
provided by the Hermes VM.

The Hermes VM may use this function to "ask" the integrator to run some
arbitrary task when the integrator has exclusive control of the runtime.
Notably, this is useful for the Hermes implementation of Workers, where
the Worker thread may ask the integrator to process an event.

Differential Revision: D91905969

Author: tsaichien

packages/react-native/ReactCommon/jsi/jsi/hermes-interfaces.h

@@ -26,6 +26,34 @@ namespace debugger {
 class Debugger;
 }
 
+#ifdef JSI_UNSTABLE
+struct IEventLoopControl {
+  /// `scheduleCallback` is an integrator-provided function for the VM to
+  /// schedule a callback task \p callback. This API must be thread-safe and run
+  /// the callback when it is the exclusive user of the Runtime.
+  virtual void scheduleCallback(const std::function<void()> callback) = 0;
+
+ protected:
+  ~IEventLoopControl() = default;
+};
+
+struct JSI_EXPORT ISetEventLoopControl : public jsi::ICast {
+ public:
+  static constexpr jsi::UUID uuid{
+      0x7b6902e6,
+      0xfd38,
+      0x11f0,
+      0x8de9,
+      0x0242ac120002};
+
+  /// Configures the eventloop control mechanism using \p eventLoopControl.
+  virtual void setEventLoopControl(IEventLoopControl* eventLoopControl) = 0;
+
+ protected:
+  ~ISetEventLoopControl() = default;
+};
+#endif
+
 /// Interface for Hermes-specific runtime methods.The actual implementations of
 /// the pure virtual methods are provided by Hermes API.
 class JSI_EXPORT IHermes : public jsi::ICast {