The scripts affect files in external/icu, bionic
and the generated files affect libcore. The files must
be updated together so there is no "obvious" home.
OEM developers seem to want to update ICU
themselves and have been asking how. Moving the
scripts to external/icu and splitting the ICU generation
code into a sub-script they can run makes some sense.
Bug: 23419215
Change-Id: Ia26fa526fd2b560a79f36d327a10e262a85db752
ac77536b79