Move CopyJob to optimized FileUtils.copy().

This new API tries its best to use optimized in-kernel copying
whenever possible, resulting in typical speed improvements of 50%!

However, since reading/writing is now the same step in the
kernel, we can't differentiate between reading/writing errors, so
report them both as Metrics.SUBFILEOP_WRITE_FILE.

Test: bit FrameworksCoreTests:android.os.FileUtilsTest
Test: vogar --mode app_process --benchmark frameworks/base/core/tests/benchmarks/src/android/os/FileUtilsBenchmark.java
Bug: 71932978
Change-Id: Ic203ef7dcb7b8a7c56084c2474cc643784e23d9d