[monodroid] Add support for the Android TimeZone file format.

[monodroid] Add support for the Android TimeZone file format.

Fixes #657609.

Android uses "ye standard" timezone file format, but instead of using
a directory + file structure as libc uses, they throw everything into
two files, a "zoneinfo.dat" and a "zoneinfo.idx", where "zoneinfo.dat"
is the concatenation of all the TZIF files and "zoneinfo.idx" contains
the timezone names and offsets into "zoneinfo.dat".  From the
ZoneInfoDB documentation:

	However, to conserve disk space the data for all time zones
	are concatenated into a single file, and a second file is
	used to indicate the starting position of each time zone
	record.  A third file indicates the version of the zoneinfo
	databse used to generate the data.

TimeZoneInfo.Android.cs is a C# port of the corresponding Android
ZoneInfoDB type so that Mono can use Android's timezone DB.