Missing instrumented files when --experimental_split_coverage_postprocessing flipped

### Description of the bug:

When --experimental_split_coverage_postprocessing is turned on only `coverage manifest` `coverage dir` and `_lcov_merger runfiles` are input to the action. There are two problems with this; one it doesn't match the behavior of unified when the flag is turned off, and second is that some toolings require instrumented files to be present on disk/sandbox to perform some calculations.

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

Run https://github.com/aspect-build/rules_js/pull/991

### Which operating system are you running Bazel on?

darwin/arm64

### What is the output of `bazel info release`?

release 6.0.0

### 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 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?

_No response_

Start by reproducing the behavior with rules_js pull request 991 and the --experimental_split_coverage_postprocessing flag. Compare the inputs passed to coverage manifest, coverage dir, and _lcov_merger runfiles with unified behavior when the flag is off; done means instrumented files are available in the action sandbox as required by the affected tooling.

Written by the indexing model from the issue text.