Deprecate RCTHostRuntimeDelegate and merge into RCTHostDelegate (react#54915)

Summary:
Currently, there are two delegate protocols related to the `RCTHost` class that Frameworks can use: `RCTHostDelegate` and `RCTHostRuntimeDelegate`.
`RCTHostDelegate` is easy to set and use as `RCTReactNativeFactory` already conforms to it. However, using the `RCTHostRuntimeDelegate` is less convenient because it can only be set via the host's `runtimeDelegate` property. This requires access to the host instance first, which in turn means having to wait for `hostDidStart` (see how we currently do this in Expo: https://github.com/expo/expo/blob/cacd14059830c00971d90d39cf8aa9e67f5e6de1/packages/expo/ios/AppDelegates/ExpoReactNativeFactory.mm#L28-L36).
Additionally it's not clear that `hostDidStart` is called before `host:didInitializeRuntime`, especially since both are called from different threads. Relying on this ordering feels unsafe to me.
I'm proposing to merge `RCTHostRuntimeDelegate` into `RCTHostDelegate` as they effectively serve the same purpose.

As part of this change, I've deprecated `RCTHostRuntimeDelegate` and its method. It can be removed in 0.85 or 0.86, depending on which release allows breaking changes. Instead, I've added the same method (optional) to `RCTHostDelegate`.

All call sites and tests have been updated accordingly.

## Changelog:

[IOS] [DEPRECATED] - Deprecate `RCTHostRuntimeDelegate` and merge into `RCTHostDelegate`

Pull Request resolved: react#54915

Test Plan:
- Manually added `host:didInitializeRuntime:` to `RCTReactNativeFactory` and confirmed it gets called
- Tested this change in Expo and our own factory
- Native unit tests are passing (for both the deprecated and new method)

Reviewed By: cortinico

Differential Revision: D94076719

Pulled By: cipolleschi

fbshipit-source-id: 946d701727eb46653ce083b66875f9b57baf5743

Author: tsapeta

packages/react-native/ReactCommon/react/runtime/iostests/RCTHostTests.mm

@@ -162,6 +162,17 @@ - (void)testDidReceiveErrorStack
 }
 
 - (void)testDidInitializeRuntime
+{
+  auto hermesRuntime = facebook::hermes::makeHermesRuntime();
+  facebook::jsi::Runtime *rt = hermesRuntime.get();
+
+  id<RCTInstanceDelegate> instanceDelegate = (id<RCTInstanceDelegate>)_subject;
+  [instanceDelegate instance:[OCMArg any] didInitializeRuntime:*rt];
+
+  OCMVerify(OCMTimes(1), [_mockHostDelegate host:_subject didInitializeRuntime:*rt]);
+}
+
+- (void)testDidInitializeRuntime_DEPRECATED
 {
   id<RCTHostRuntimeDelegate> mockRuntimeDelegate = OCMProtocolMock(@protocol(RCTHostRuntimeDelegate));
   _subject.runtimeDelegate = mockRuntimeDelegate;

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTHost.h

@@ -49,11 +49,24 @@ typedef NSURL *_Nullable (^RCTHostBundleURLProvider)(void);
                exceptionId:(NSUInteger)exceptionId
                    isFatal:(BOOL)isFatal
                  extraData:(NSDictionary<NSString *, id> *)extraData __attribute__((deprecated));
+
+/**
+ Delegate method invoked after the host has finished initializing the JavaScript runtime. At this stage,
+ bindings for Turbo Modules and the NativeComponentRegistry are already installed,
+ but the JavaScript bundle has not yet been executed. This method is called on the JavaScript thread;
+ accessing the runtime from any other thread is prohibited and will result in crashes.
+ */
+- (void)host:(RCTHost *)host didInitializeRuntime:(facebook::jsi::Runtime &)runtime;
+
 @end
 
-@protocol RCTHostRuntimeDelegate <NSObject>
+// `RCTHostRuntimeDelegate` has been merged into `RCTHostDelegate` in 0.84
+[[deprecated("Use 'RCTHostDelegate' instead")]]
+@protocol RCTHostRuntimeDelegate<NSObject>
 
-- (void)host:(RCTHost *)host didInitializeRuntime:(facebook::jsi::Runtime &)runtime;
+- (void)host:(RCTHost *)host
+    didInitializeRuntime:(facebook::jsi::Runtime &)runtime
+    [[deprecated("Use an equivalent method from 'RCTHostDelegate' instead")]];
 
 @end
 
@@ -84,7 +97,8 @@ typedef std::shared_ptr<facebook::react::JSRuntimeFactory> (^RCTHostJSEngineProv
 - (instancetype)init NS_UNAVAILABLE;
 + (instancetype)new NS_UNAVAILABLE;
 
-@property (nonatomic, weak, nullable) id<RCTHostRuntimeDelegate> runtimeDelegate;
+@property (nonatomic, weak, nullable) id<RCTHostRuntimeDelegate> runtimeDelegate
+    [[deprecated("Use 'RCTHostDelegate' instead")]];
 
 @property (nonatomic, readonly) RCTSurfacePresenter *surfacePresenter;
 

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTHost.mm

@@ -371,7 +371,14 @@ - (BOOL)instance:(RCTInstance *)instance
 
 - (void)instance:(RCTInstance *)instance didInitializeRuntime:(facebook::jsi::Runtime &)runtime
 {
+  if ([_hostDelegate respondsToSelector:@selector(host:didInitializeRuntime:)]) {
+    [_hostDelegate host:self didInitializeRuntime:runtime];
+  }
+  // Runtime delegate is deprecated as of 0.84
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
   [self.runtimeDelegate host:self didInitializeRuntime:runtime];
+#pragma clang diagnostic pop
 }
 
 - (void)loadBundleAtURL:(NSURL *)sourceURL