AndroidInputEventProtoConverter: Move impl into templated header

Move the AndroidInputEventProtoConverter implementation into the header
and make it a templated class so that the auto-generated proto classes
from Perfetto do not need to be relied upon for testing.

Bug: 391468016
Test: Presubmit
Flag: EXEMPT refactor
Change-Id: I03e0960f6ef46428b919aac80c6bbb470db30c89