Expose Process.isIsolated()

Rather than have a process attempt to perform IO / IPC and check if it
fails, it makes much more sense to expose this getter.

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: 73343822
Test: Same code that's used in Chrome via reflection.
Change-Id: I1505962679da36ac42401230b204bff7b3376b73