Switch Utils.formatElapsedTime to use ICU's MeasureFormat

Previously, localizable strings were used instead, causing various
difficulties and inconsistencies.

Now we use ICU's MeasureFormat. The results for English are almost
identical to the previous results (see below), and we also get higher
quality and better-vetted results for other locales.

Note: This also makes formatted strings shorter by eliminating zeros.
For example, what was previously shown as "2d 0h 15m" is now shown as
"2d 15m".

Bug: 36994779
Bug: 37701311
Test: make -j RunSettingsRoboTests
Change-Id: I78fd09e4e7f63f41ef88d3d3fc4ba2be15e1d812