feat(react-native-host): expose auxiliary RCTTurboModuleManagerDelegate via RNXHostConfig (2/3)

[Saadnajmi]

Description

Depends on #4144

Adds an optional turboModuleManagerDelegate property to RNXHostConfig that lets consumers participate in TurboModule construction without replacing RNXTurboModuleAdapter.

Motivation

RNXTurboModuleAdapter is rnx-kit's RCTTurboModuleManagerDelegate. Today it owns the full TurboModule construction path:

• getModuleClassFromName: falls back to RCTCoreModulesClassProvider
• getModuleInstanceFromClass: falls back to RCTAppSetupDefaultModuleFromClass

For modules that need per-host state — e.g., an RCTExceptionsManager initialized with a per-host delegate, or an RCTDevSettings with a custom data source — there's no extension
point. In bridge mode this case is handled via RCTBridgeDelegate.extraModulesForBridge: (the bridge prefers pre-constructed instances vended there). In bridgeless mode, that hook
isn't called — modules go through RCTTurboModuleManager.delegate instead.

Design

RNXHostConfig adds:

@property (nonatomic, readonly, weak, nullable) id<RCTTurboModuleManagerDelegate> turboModuleManagerDelegate;

RNXTurboModuleAdapter adds a hostConfig weak reference and, for each RCTTurboModuleManagerDelegate method it implements, consults the auxiliary via respondsToSelector: first;
returning nil / Nil falls through to the existing default behavior.

- (Class)getModuleClassFromName:(char const *)name {
    id<RCTTurboModuleManagerDelegate> aux = _hostConfig.turboModuleManagerDelegate;
    if ([aux respondsToSelector:_cmd]) {
        Class cls = [aux getModuleClassFromName:name];
        if (cls != Nil) return cls;
    }
    return RCTCoreModulesClassProvider(name);
}

Same shape for getModuleInstanceFromClass:.

Properties

• Symmetric with bridge-mode extraModulesForBridge:: the per-host injection point that bridge consumers use.
• Backward-compatible: consumers that don't implement turboModuleManagerDelegate see no behavior change.
• Generic, not per-method: any current or future RCTTurboModuleManagerDelegate method (getModuleProvider:, getTurboModule:jsInvoker:, etc.) the consumer implements is routed
  automatically — no per-hook plumbing required in rnx-kit.
• Zero overhead when the auxiliary delegate doesn't respond — single respondsToSelector: check.

Example

@interface MyHostConfig : NSObject <RNXHostConfig, RCTTurboModuleManagerDelegate>
@end

@implementation MyHostConfig {
    MyExceptionsManagerDelegate *_exceptionsDelegate;
}

- (id<RCTTurboModuleManagerDelegate>)turboModuleManagerDelegate {
    return self;
}

// Required RCTTurboModuleManagerDelegate methods — return nil to defer to rnx-kit's defaults.
- (Class)getModuleClassFromName:(const char *)name { return Nil; }

- (id<RCTTurboModule>)getModuleInstanceFromClass:(Class)cls {
    if (cls == [RCTExceptionsManager class]) {
        return [[RCTExceptionsManager alloc] initWithDelegate:_exceptionsDelegate];
    }
    return nil;
}
@end

Test plan

Tested internally