[core][iOS] Clean up ExpoModulesCore.podspec

[tsapeta]

Why

The podspec got a bit messy over time. Now we can include Fabric-specific code as Fabric pods are installed by default anyway.

How

• Moved requiring RN scripts to the top (pod ipc spec was failing because we're requiring it after we call add_dependency)
• Cleaned up compiler flags and xcconfigs
• Removed using vendored frameworks (we don't prebuild the modules core)
• Added React-RCTFabric dependency even if Fabric is not enabled
• Always include ios/Fabric and common/fabric folders
• Replaced the legacy RN_FABRIC_ENABLED with RCT_NEW_ARCH_ENABLED

Test Plan

• bare-expo builds and runs just fine
• iOS Client on EAS Build check is failing, but it's unrelated (and also broken on main)

[expo-bot]

The Pull Request introduced fingerprint changes against the base commit: df90d60

Fingerprint diff

[
  {
    "op": "changed",
    "source": {
      "type": "dir",
      "filePath": "../../packages/expo-modules-core",
      "reasons": [
        "expoAutolinkingIos",
        "expoAutolinkingAndroid"
      ],
      "hash": "5c83c424bda454efb2cebcb5c21dccde1421d079"
    }
  },
  {
    "op": "changed",
    "source": {
      "type": "dir",
      "filePath": "ios",
      "reasons": [
        "bareNativeDir"
      ],
      "hash": "d6c2df3f5627709a916dc8bfac3acc837a857ffc"
    }
  }
]

---

Generated by PR labeler 🤖

[Kudo]

much appreciated for the change. leaving some comments for possibly improvements

[Kudo]

Suggested change

'"$(PODS_ROOT)/Headers/Private/Yoga"', # Expo.h -> ExpoModulesCore-umbrella.h -> Fabric ViewProps.h -> Private Yoga headers

maybe we don't need Yoga because react-native core will add Yoga for modules

[tsapeta]

Sadly, it fails on compiling AppDelegate.mm – it can't find <yoga/style/Style.h> 🤔 I'll investigate this later and for now I would just go ahead and merge it as is.