Handle edge-to-edge when it's not enabled by gradle property

[zoontek]

Summary:

On Android 15 (API 35), edge-to-edge is enforced by default unless the app explicitly opts out via windowOptOutEdgeToEdgeEnforcement. On Android 16+, it's always enforced regardless.

Previously, edge-to-edge behavior was only driven by the edgeToEdgeEnabled gradle property, meaning apps on Android 15+ could be in edge-to-edge mode without React Native being aware of it, leading to incorrect insets / layout behavior.

This PR introduces isEdgeToEdge, a computed value that accounts for the OS-level enforcement in addition to the gradle flag, and replaces most usages of isEdgeToEdgeFeatureFlagOn with it. A new initEdgeToEdge(context, flag) function replaces setEdgeToEdgeFeatureFlagOn() and reads the theme attribute to detect opt-out on API 35.

Changelog:

[ANDROID] [FIXED] - Handle edge-to-edge when it's not enabled by the edgeToEdgeEnabled gradle property but enforced by the OS (Android 15+)

Test Plan:

• Verify on Android 15 device/emulator without edgeToEdgeEnabled = true: isEdgeToEdge should be true (unless opted out via theme attribute).
• Verify on Android 16+ device/emulator: isEdgeToEdge should always be true.
• Verify on Android 14 and below without the flag: isEdgeToEdge should be false.
• Verify with edgeToEdgeEnabled = true: behavior unchanged, isEdgeToEdge is true on all API levels.