Add experimental support for stripping config prefixes from output paths.

This applies to executor actions, not paths on the Blaze machine.

For example:

BEFORE: foo/bar bazel-out/x86-opt/bin/baz -o bazel-out/x86-opt/bin/out
AFTER:  foo/bar bazel-out/bin/baz -o bazel-out/bin/out

This promises better caching for actions that don't depend on the CPU (or whatever else appears in the "/x86-opt/" path segment).

This is a first-pass implementation that takes a heuristic approach by textually searching and removing config prefixes from command line strings. This logic is centralized in the new class PathStripper.

A natural followup would be to explore if we can exploit CustomCommandLine, which stores paths as Artifacts until just before execution, to strip paths directly. This would be a more structured approach. ArtifactExpander may help. Care would be needed to only invoke this on supporting executors.

For https://github.com/bazelbuild/bazel/issues/6526.

PiperOrigin-RevId: 375804248