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

The strings are used by android.webkit.DateSorter only, but loading
the data in every LocaleData.get bares a cost in both memory and load
time. Now loads the data only when DateSorter is initialized.

Bug: 138994281
Bug: 144560585
Test: atest CtsLibcoreTestCases:libcore.libcore.icu.LocaleDataTest
Change-Id: I19efc3e068ec81e3276b6666aa0e5ba272e28dee
4 files changed