Remove inner class for bundle key to follow conventions

- Update constant value as per go/android-api-guidelines#constants-keys.
- Also adding a deprecated version that the manager still publishes for backward
compatibility with older app implementations depending on this hidden key, like AICore.

Bug: 430118901
Test: CTS
Flag: android.app.ondeviceintelligence.flags.on_device_intelligence_25q4
Change-Id: Ie78c9cb78ccd72871c5f784562d8483a22a2969e