Limit the maximum size of small notification icons

Right now, the size of small notification icons is unbounded and can cause big memory usage spikes (easily measured as 50MB+). This limits the maximum size of small icon when its set as a bitmap.

Bug:193720474
Bug:209044537

Test: manual via test app
Test: atest NotificationTest
Change-Id: I684fe29d5b473d86280035e00298c8e59f47dbb7