hugolib: Fix multilingual single-host alias generation

[jmooring]

While PR #14386 corrected alias publication paths for monolingual and multilingual multihost configurations, multilingual single-host sites still exhibit incorrect alias publication paths under certain conditions.

1. When an alias path in front matter is absolute, the alias is incorrectly published relative to the publishDir. It should be published relative to the site root.

   content path	front matter alias	expected publication path	actual publication path
   content/fr/foo/s1/p1.md	/p1-alias	public/fr/my-alias/index.html	public/my-alias/index.html

   That means, for example, that aliases for French content are clobbered by aliases for German content. Yes, this is a breaking change, but what we have is already broken.

2. When an output format has a non-empty path parameter, the path directory is incorrectly created in the root of the publishDir. It should be published in the site root. Consider an output format where the path is set to print:

   content path	front matter alias	expected publication path	actual publication path
   content/fr/foo/s1/p1.md	p1-alias	public/fr/print/foo/s1/p1-alias/index.html	public/print/fr/foo/s1/p1-alias/index.html

Note

As of v0.153.0, the site root may be composed of language, role, and/or version. For example, public/guest/v1.0.0/fr.

[jmooring]

cc: @chalin