Use Apple unified logging API (os_log) (#27892)

Summary:
As discussed in https://github.com/facebook/react-native/issues/27863, the following changes were made to modernize the internal default logging function:

- `RCTDefaultLogThreshold` is now set to `RCTLogLevelTrace` in both release and debug builds—the Apple logging system will discard uncollected log entires, while allowing for collection when needed
- `RCTLogLevel` is translated to the appropriate log type
- The log subsystem is "com.facebook.react.log"
- `RCTLogSource` translates to the appropriate category ("native"/"javascript")
- Log the provided message using `os_log_with_type`

Closes https://github.com/facebook/react-native/issues/27863

## Changelog

[iOS] [Changed] - Use Apple unified logging API (os_log)
Pull Request resolved: https://github.com/facebook/react-native/pull/27892

Test Plan:
## From Original PR

Ran a test app in the iOS simulator, and verified that logs are correctly displayed in Console.app as well as using the following command:
```sh
/usr/bin/xcrun simctl spawn booted log stream --level debug --style compact --predicate 'process=="ReactNativeTesterApp" && subsystem=="com.facebook.react.log"'
```

## Peter's Test Plan

1. Apply P125583473
2. Verify log output in Xcode P125583504
3. Apply this diff
4. Verify log output in Xcode P125583597

These appear unchanged, after digging into why, I realized that FB doesn't even use the default log function, we inject a custom one [here](https://fburl.com/diffusion/887a1axs). So this PR shouldn't affect us at all. :)

Differential Revision: D19605414

Pulled By: PeteTheHeat

fbshipit-source-id: 1d70fb702c337a759905d4a65a951a31353ce775