Truncate long device admin descriptions

Limit the length of the description loaded from a device admin's
manifest to a maximum of 8192 characters. This prevents potential issues
with excessively long descriptions. Cherry picked the main CL to fix the
order

Bug: 492093013
Test: manual
Flag: EXEMPT BUGFIX
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:f1ed046d2c48a38b9a800ef6a86cc14d3ab312a3
Security vulnerability cherry pick for https://b.corp.google.com/issues/492093013
Topic: https://googleplex-android-review.git.corp.google.com/q/topic:%22b492093013%22
#b/492093013
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:bace39bacf296b95a71f7bff1f87f68e39178874
Merged-In: I06b621e37d97fd8554172c2446e2838dfaccc104
Change-Id: I06b621e37d97fd8554172c2446e2838dfaccc104