Use ICU data for time zone name parsing.

Use ICU time zone names in DateTimeFormatterBuilder to parse time zone
names and IDs (formatting was done in a previous commit).

Also remove built-in alias and metazone data from ZoneNames and use ICU
data directly.

Don't provide GMT+0 and GMT-0 zone ids from the IcuZoneRulesProvider, as
those are not parseable by ZoneId.

Also improve time zone formatting to print generic GMT string, if no
name is available.

Bug: 28832222
Test: compiles, tests follow later.
Change-Id: Ifea756ff5163dbd032960d82e88da9dfee1ff0cc