`remoteActionBuildingSemaphore` slows down highly parallel remote builds

### Description of the bug:

Highly parallel RBE builds are slower than they need to be because of `remoteActionBuildingSemaphore`.

### Which category does this issue belong to?

Remote Execution

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

Have a build that can do 300+ actions at once, use `--jobs=300`, and a host machine with 24 or fewer threads. Build clean once with Bazel 7.0.0. Build clean once with `remoteActionBuildingSemaphore` usage commented out. Compare and see that the second build is faster.

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

Ubuntu 22.04

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

development version

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

Built the `release-7.0.0` branch and modified it per above.

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

_No response_

### Is this a regression? If yes, please try to identify the Bazel commit where the bug was introduced.

_No response_

### Have you found anything relevant by searching the web?

https://github.com/bazelbuild/bazel/pull/17120 / https://github.com/bazelbuild/bazel/commit/4069a87611886532a19c7e558ab4c2f1e83f53f0 added the semaphore

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

_No response_