[7.1.0] Set the executable bit on files in output directories uploaded to a...

[7.1.0] Set the executable bit on files in output directories uploaded to a disk or remote cache. (#21376)

Bazel doesn't preserve executable bits for outputs; all files in the
output tree are chmodded to either 0555 or 0755 after action execution,
depending on --experimental_writable_outputs.

With respect to the disk/remote cache protocol, Bazel always marks
uploaded inputs as executable and always ignores the executable bit on
downloaded outputs. For uploaded outputs, the behavior currently differs
between directories and non-directories; this CL makes the behavior
consistent.

This makes it more likely that the input Merkle tree to a remote action
can hit a cache populated by a previous local action. (See unknown
commit where the behavior was changed for non-directory outputs, with
the same rationale.)

As a minor effect, it also avoids additional I/O to obtain the
permission bits from the filesystem, which adds up for very large tree
artifacts.

PiperOrigin-RevId: 607367059
Change-Id: Ib507a98f32c0a5c89b1ed0f1ec3777f1c6430e28