An esbuild rule that ran fine in a local repo (eg bazel build //:my_esbuild_rule)
fails when built externally (eg bazel build @other_workspace//:my_esbuild_rule).
By prepending the workspace root to the bin path, the resulting base
URL works correctly in both local and remote repo invocations, allowing
esbuild output to be consumed by a different repo.
This change fixes remote repos in Bazel 4.0.0. 3.7.0 seems to require a
workspace_root.replace("external/", "") call first in order
to get the correct location. So while this patch should not break anything
that was not already broken, it only fixes/adds support for remote repos
in 4.0+.
