Closes #14122.
Adds two extensions to `--allow-run` behaviour:
- When `--allow-run=foo` is specified and `foo` is found in the `PATH`
at startup, `RunDescriptor::Path(which("foo"))` is added to the
allowlist alongside `RunDescriptor::Name("foo")`. Currently only the
latter is.
- When run permission for `foo` is queried and `foo` is found in the
`PATH` at runtime, either `RunDescriptor::Path(which("foo"))` or
`RunDescriptor::Name("foo")` would qualify in the allowlist. Currently
only the latter does.
