ZipUtils: use FileChannel#size

RandomAccessFile#length returns 0 for block devices while
FileChannel#size returns the correct size. ZipUtils should work with
block-device zip files when Android is running as a guest OS and
APK/APEX files are passed via block devices.

Bug: 193592496
Bug: 192366904
Test: FrameworksServicesTests
Change-Id: I6472e2a9051b92a5a778b4990b8e681492985d1a