Update DroidSansFallback typeface + preserve legacy version

Move the Droid Sans Fallback typeface from Eclair and earlier Android versions
to a new path in the tree, and update the mainline version to add 4,398 Hanzi
characters, which adds approximately ~0.5 MB to the system footprint.

If that additional size is problematic, implementors may elect to build instead
with the legacy version, which supports GB2312 for Simplified Chinese but lacks
the expanded character set.