Fix two StrictMode stack collection bugs.

When Binder calls are nested, we can quickly end up with a snowball
of stacktraces that can cause the original transaction to fail.  This
CL makes two specific changes to alleviate this pressure:

-- Consider a nested Binder call from PID A -> B -> C.  If both B and
C encounter dozens of StrictMode violations, then gatheredViolations
in B will end up with 10 ViolationInfo (5 from B and 5 from C).  This
problem only grows with each successive nested call.  To solve this,
always limit ourselves to only ever write out 3 ViolationInfo from
any given process.

-- CrashInfo already nicely truncates any large stack traces to 20kB,
but readAndHandleBinderCallViolations() blindly appends the entire
local trace, and never considers truncating again.  Similar to the
first problem above, nested calls can quickly cause the stackTrace
value to explode in size.  To solve this, we always re-truncate the
stackTrace value after appending our local stack.

Also fix some NPE bugs when missing crashInfo.

(cherry-picked from commit 58f27b50)

Test: builds, boots
Bug: 32575987
Change-Id: Ie8373ca277296f920f2b1c564d419c702a8ee0f2