Add support for new tzlookup.xml attribute

Add support for new tzlookup.xml attribute for country elements:
defaultBoost is used to customize the time zone detection behavior for
some countries.

Test: atest libcore.libcore.timezone
Bug: 141727033
Bug: 141740972
Change-Id: Ic0b20fcbb8dfc6c03d602e6e52c6427964880b91
6 files changed