Increase default user icon size.

This increases the size of the default user icon to 190dp.

A new method convertToBitmapAtUserIconSize is added to UserIcons to
allow bitmaps of this size to be easily obtained. The existing
method convertToBitmap uses the intrinsic size of the drawable, which
is only 48dp as standard.

Bug: 218838295
Test: visual inspection of user icon for owner and new users
Test: atest UserIconsTest
Change-Id: I5cbf110731f4c944bb1d3af63b5a0fcb5ab50f16