Extract variables related to Emoji to a separate class.

Looks like not all JDKs support Emoji patterns (introduced in UTK51). Once
we first invoke a method (even static, even unrelated to Emoji) in
`PeopleTileViewHelper`, for those JDKs which do not have the support,
the method invoke would not be successful. This CL extracts the Emoji
pattern compilation to a separate class, which delays the pattern
compilation only when it is necessary.

Test: atest -c SystemUIGoogleRoboRNGTests:com.android.systemui.people.PeopleSpaceScreenshotTest
Change-Id: Ic408374fc30f849eedbb60c6f470e432c46d0576