Adding View.setTooltip/getTooltip and 'tooltip' layout attribute.
Following Material Design spec for styles and behavior.
Bug: 31515376
Test: cts-tradefed run singleCommand cts -m CtsViewTestCases
--test android.view.cts.TooltipTest
Change-Id: I2d2527f642cd7446ffc88d4beffc7b81d7a2f6d6