Provide NavGraphImpl

Moving all common code to the common source set and allowing the
specific platforms to use that source.

RelNote: N/A
Test: all tests pass
Bug: 403616316
Change-Id: If77617d32d274ea2f5f76107336293b562fda300

• navigation/navigation-common/bcv/native/current.txt[diff]
• navigation/navigation-common/src/androidMain/kotlin/androidx/navigation/NavGraph.android.kt[diff]
• navigation/navigation-common/src/commonMain/kotlin/androidx/navigation/internal/NavGraphImpl.kt[Added - diff]
• navigation/navigation-common/src/nonAndroidMain/kotlin/androidx/navigation/NavGraph.nonAndroid.kt[diff]