Pass valid file descriptor to binder

screenshotFd needs to be optional in Bugreport API. For some bugreports
such as wifi,telephony, interactive etc taking a screenshot is not
required.

Initially, the API was sending invalid file descriptor to the Binder, but
that binder transaction could not be completed as Binder validates the
file descriptor to be valid and not-null.

Adding a tmp.png screenshot file to pass to bugreport API call. In a
separate CL in frameworks/native, added check that the bugreports that
don't require screenshots would not use this file descriptor value.

Bug: 128981582
Test: Tested by taking bugreports using Bugreport API in shell
Merged-In: I3233f5753506ae159c9fa591742e6b99e361039b
Change-Id: I3233f5753506ae159c9fa591742e6b99e361039b