Add app_compat_overrides to WritableNamespaces and clean up WritableFlags

This commit updates the allowlist of DeviceConfig namespaces that
can be written with the WRITE_ALLOWLISTED_DEVICE_CONFIG permission
to include app_compat_overrides namespaces.

Bug: 392162661
Flag: android.security.protect_device_config_flags
Test: atest DeviceConfigApiTests

Change-Id: I5a0f2f9cfec7e4b91317c7d4745ebc542885f956