Scale tracker icon to desired height and ensure aspect ratio.

Also `setAutoMirrored(true)`. The auto mirroring works now that the
canvas is translated to the tracker position.

Flag: android.app.api_rich_ongoing
Fix: 375251723
Fix: 372909308
Test: post a ProgressStyle Notification. (patch ag/29870217 to post.)
Test: patch ag/30006048 and run ProgressStyleNotificationScreenshotTest
Change-Id: I2e9036aef26b7839dfc387509a40a2a30b0a3679