Migrate from `PrivateSentrySDKOnly` to `SentryObjCSDK.internal`

[philprime]

sentry-cocoa 9.19.0 introduces a new structured hybrid SDK API via SentrySDK.internal (Swift) and SentryObjCSDK.internal (ObjC). The old PrivateSentrySDKOnly class is deprecated and will be removed in the next major version.

Implementation PR: getsentry/sentry-cocoa#8097
Design doc: SENTRY-INTERNAL-API.md

Benefits

• Eliminates 3 internal header imports. Drop PrivateSentrySDKOnly.h, SentryOptionsInternal.h, and Sentry-Swift.h. The new API is fully public via <SentryObjC/SentryObjC.h>.
• No more NSClassFromString / performSelector: hacks. Unity previously used NSClassFromString(@"SentryId") as a workaround for SentryId living in the Swift bridging header. The new ObjC API provides SentryObjCId and SentryObjCSpanId as proper ObjC types.
• No more SentryOptionsInternal.h. The +initWithDict:didFailWithError: method is now [[SentryObjCSDK internal] optionsFromDictionary:error:].
• SPM / xcframework compatible. Works with binary distribution — no exposed private headers.

Import Change

iOS (Plugins/iOS/SentryNativeBridge.m)

// Before
#import <Sentry/Sentry-Swift.h>
#import <Sentry/PrivateSentrySDKOnly.h>
#import <Sentry/SentryOptionsInternal.h>

// After — single import, no internal headers
#import <SentryObjC/SentryObjC.h>

macOS (Plugins/macOS/SentryNativeBridge.m)

The macOS bridge currently loads classes dynamically via NSClassFromString:

// Before
static Class SentryOptionsInternal;
static Class PrivateSentrySDKOnly;
LOAD_CLASS_OR_BREAK(SentryOptionsInternal)
LOAD_CLASS_OR_BREAK(PrivateSentrySDKOnly)

// After — direct import, no dynamic loading needed
#import <SentryObjC/SentryObjC.h>
// Use [SentryObjCSDK internal].* directly

Key Changes

• [SentryOptionsInternal initWithDict:dict didFailWithError:&error] → [[SentryObjCSDK internal] optionsFromDictionary:dict error:&error]
• [PrivateSentrySDKOnly setSdkName:@"sentry.cocoa.unity"] → [SentryObjCSDK internal].sdk.name = @"sentry.cocoa.unity"
• [PrivateSentrySDKOnly installationID] → [SentryObjCSDK internal].sdk.installationID
• [PrivateSentrySDKOnly setTrace:traceId spanId:spanId] → [[SentryObjCSDK internal] setTrace:traceId spanId:spanId]
• [PrivateSentrySDKOnly captureEnvelope:envelope] → [[[SentryObjCSDK internal] envelope] capture:envelope]
• NSClassFromString(@"SentryId") → SentryObjCId (proper ObjC type)
• NSClassFromString(@"SentrySpanId") → SentryObjCSpanId (proper ObjC type)

Affected Files (as of latest main)

• package-dev/Plugins/iOS/SentryNativeBridge.m — direct imports + call sites
• package-dev/Plugins/macOS/SentryNativeBridge.m — dynamic class loading + performSelector:
• src/Sentry.Unity.Editor.iOS/NativeOptions.cs — C# code gen emitting ObjC
• src/Sentry.Unity.Editor.iOS/NativeMain.cs — C# code gen emitting import

Checklist

• Replace all PrivateSentrySDKOnly / SentryOptionsInternal call sites with [SentryObjCSDK internal].*
• Remove Sentry-Swift.h import — use SentryObjCId / SentryObjCSpanId instead
• Remove dynamic class loading (NSClassFromString) for SentryOptionsInternal and PrivateSentrySDKOnly on macOS
• Update C# code generators (NativeOptions.cs, NativeMain.cs) to emit new ObjC API
• Change all imports to #import <SentryObjC/SentryObjC.h>
• Bump minimum sentry-cocoa dependency to 9.19.0+
• Run full test suite to verify no regressions

[linear-code]

UNITY-227