Make isInteractive(display) a testAPI

The API would be required in CTS to check the interactiveness of individual displays. In case of MUMD (multi user multi display) devices, it is possible that only one display (ex. driver display) is off, and PM#isInteractive returns true.

Flag: NONE hidden to test API

Bug: 369415968
Test: m
Change-Id: Id0d194984e37779c805eed8509025e43fccb89f1