Expand formatSimple() to support widths.

One of the highest-traffic users of String.format() is in the
notification code, which uses argument widths.  To support these
use-cases, this change adds argument width support, with tests.

Bug: 170978902
Test: atest error_prone_android_framework_test
Exempt-From-Owner-Approval: trivial additions
Change-Id: I8e36d4725a6d0cc896dedc5c457eb5f38486d7b6