[CD Cursor] Devopts override for connected displays flag

Add and use a sysprop based override for connected displays cursor flag.
Override is expected to require an restart on change. Allowing us to
cache its value.

Test: atest inputflinger_tests
Bug: 362719483
Flag: com.android.input.flags.connected_displays_cursor

Change-Id: I8634e61eb57c82b2b4c904239a4d407ce69f97d8