libsparse: Fix allocation failures on 32-bit systems.

libsparse uses mapped files for length computation checks and writing
output data. The platform-tools package for Windows is 32-bit, and if
an embedded file in the stream is large enough, mapping will fail. In
theory, this failure mode could happen on 64-bit systems as well.

As a workaround, map files in chunks of 256MB instead. This is
implemented by adding a new "fd_chunk" callback to the sparse ops
struct.

Bug: 273933042
Bug: 268872725
Test: fastboot update on Windows
Change-Id: Ic40696b34a1d0951787c899db701fc2fa204eb18