experimental_action_listener config variable is set to "null" instead of "[]" in exec configuration

[eric-skydio]

Description of the bug:

In the configuration associated with CoreOptions there is a configuration value experimental_action_listener: [] associated with the (deprecated) command-line flag --experimental_action_listener. We do not use this functionality, and have no desire to do so.

Unfortunately, after any transition to exec configuration, this value appears to change from [] to null, and there is no way to transition it back from Starlark code.

The reason this is a problem is related to our desire to perform "unifying transitions" as discussed in #14023 and #14236. All of the other config set by "exec" can be controlled manually from a Starlark transition, but because this particular flag is "experimental" we can't reset it to [], so we end up with two different configuration hashes for the same configuration, and Bazel ends up building those targets and everything they depend on twice without reason.

This should be a small one-line fix, and is a blocker for many of the benefits of --experimental_output_directory_naming_scheme=diff_against_baseline, and possibly for moving to Bazel 6.x entirely, so it would be nice to get this fix backported as well.

I believe the simplest fix is a one-line change here to construct an empty list, although more complicated solutions are possible: https://github.com/bazelbuild/bazel/blob/release-6.0.0rc4/src/main/java/com/google/devtools/build/lib/analysis/config/ExecutionTransitionFactory.java#L131-L132

What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

genrule(
    name = "rule1",
    srcs = [],
    outs = ["file1.bin"],
    cmd = "echo 'echo hi' > $@",
    executable = True,
)

genrule(
    name = "rule2",
    srcs = [],
    outs = ["file2.txt"],
    cmd = 'echo "file2" > $@',
    exec_tools = [":rule1"],
)

bazel cquery "filter(rule1, deps(:all))"
This returns two different config hashes, use diff on bazel config to show the issue

<   experimental_action_listener: []
---
>   experimental_action_listener: null

Note that we're not concerned with any of the other changes in this list since they are all controllable by Starlark

Which operating system are you running Bazel on?

Ubuntu 18.04

What is the output of bazel info release?

release 6.0.0rc4

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 master; git rev-parse HEAD ?

No response

Have you found anything relevant by searching the web?

No response

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

Tagging @gregestren @sdtwigg and the Configurability team