Ensure consistency of capitalization in RelativeDateTimeFormatter

Contains refactoring. Benchmarks below to show no appreciable
negative performance impact to formatters. We do now cache a new
type of formatter.

Benchmarks measured in microseconds on mako.

Before:
DateIntervalFormat_formatDateRange_DATE 244
DateIntervalFormat_formatDateRange_DATE_TIME 256
DateIntervalFormat_formatDateRange_TIME 208

RelativeDateTimeFormatter_getRelativeDateTimeString 207.2
RelativeDateTimeFormatter_getRelativeDateTimeString_ABBREV 218.2
RelativeDateTimeFormatter_getRelativeTimeSpanString  70.5
RelativeDateTimeFormatter_getRelativeTimeSpanString_ABBREV  67.4

After:
DateIntervalFormat_formatDateRange_DATE 237
DateIntervalFormat_formatDateRange_DATE_TIME 241
DateIntervalFormat_formatDateRange_TIME 200

RelativeDateTimeFormatter_getRelativeDateTimeString 149.4
RelativeDateTimeFormatter_getRelativeDateTimeString_ABBREV 161.8
RelativeDateTimeFormatter_getRelativeTimeSpanString  71.7
RelativeDateTimeFormatter_getRelativeTimeSpanString_ABBREV  69.0

Bug: 20247811
Change-Id: I51075f89ca6b1d8862335e0e5a4d67a5624edfa6
8 files changed