Add Application.getProcessName()

This information is already available to non-sandboxed processes via
ActivityManager.getRunningAppProcesses(). However, performing an IPC and
iterating processes is quite cumbersome. See other alternatives devs have tried:

https://stackoverflow.com/questions/19631894/is-there-a-way-to-get-current-process-name-in-android

My specific motivation for exposing this information more directly is to
be able to perform process-specific initialization logic in
Application.attachBaseContext():

https://cs.chromium.org/chromium/src/chrome/android/java/src/org/chromium/chrome/browser/ChromeApplication.java?rcl=ac2e180a1265f88dd4030bb35d69f5d0b2dc488d&l=54

Bug: 73344323
Test: Same code that's used in Chrome via reflection.
Change-Id: I83cec468458078e3fa183427a039869f74539c3d