Move yesterday/today Strings from LocaleData into a new ICU class

Note that the strings are no longer cached here to avoid permanent
app Java heap growth due to strong cache. Consider that no user of DateSorter
exists in the platform, and the API is legacy. The impact on app performance
is expected to be very low.

Bug: 144560585
Bug: 138994281
Test: atest CtsWebkitTestCases:android.webkit.cts.DateSorterTest
Change-Id: I659d430901cf1838befc0a35f5188d069169e824