Clone files into the disk cache where the filesystem supports it

[ladd]

Description of the feature request:

In local testing with our iOS bazel setup, I noticed that that files copied into the local disk cache are duplicates, rather than clones. For APFS (and btrfs), copy-on-write clones will save disk space.

The current implementation uses an inputStream and can't benefit from cloning.

I've attempted a fix here:

#30776

Which category does this issue belong to?

Performance

What underlying problem are you trying to solve with this feature?

Excess disk consumption when operating on multiple worktrees locally.

Which operating system are you running Bazel on?

macOS

What is the output of bazel info release?

release 9.2.0

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse HEAD ?

$ git remote get-url origin
git@github.com:ladd/bazel.git

$ git rev-parse HEAD
0e3a10218a0abfab7c1bdd917443a0f3288383d3

Have you found anything relevant by searching the web?

Prior work on optimizing copies here:

ec90e05

Any other information, logs, or outputs that you want to share?

Local performance testing is neutral. Disk savings appear to be significant for my workloads.