The new location expansion pattern `rlocationpath` and its plural version `rlocationpaths` resolve to the path(s) suitable for the Rlocation function offered by runfiles libraries.

Compared to the `rootpath` pattern, which can returns `../repo_name/pkg/file` for a file in an external repository and `pkg/file` for a file in the main repository, the path returned by `rlocationpath` is always of the form `repo_name/pkg/file`.

RELNOTES: The new path variable `$(rlocationpath ...)` and its plural form `$(rlocationpaths ...)` can be used to expand labels to the paths accepted by the `Rlocation` function of runfiles libraries. This is the preferred way to access data dependencies at runtime and works on all platforms, even when runfiles are not enabled (e.g., on Windows by default).

Work towards bazelbuild#16124
Fixes bazelbuild#10923

Closes bazelbuild#16667.

PiperOrigin-RevId: 485930083
Change-Id: I85c0ef29c8332eeabd8473d2611ede546eb24016