Make ViewConfiguration#getMultiPressTimeout public

As part of media mainline project, we're resolving hidden API usages.
ViewConfigration#getMultiPressTimeout is a hidden API
used by MediaSessionService, which is going to move to mainline module.

Seeing a public API, ViewConfiguration#getLongPressTimeout,
making getMultiPressTimeout public seems to be trivial.

Bug: 171163798
Test: build successful

Change-Id: I4fb7b884b7496bfc0e4f33a93eb2a69a889a91c5