packages: Use origin file names as their input labels.

* guix/packages.scm (add-input-label): Rely on 'origin-actual-file-name' for
internal inputs labels.
* tests/packages.scm ("this-package-input, origin"): New test.
* doc/guix.texi (package Reference): Mention origin lookup for
‘lookup-package-input’ & co.
* gnu/packages/base.scm (tzdata)[inputs]: Reintroduce label.
* gnu/packages/tex.scm (texlive-hyphen-complete)[inputs]: Likewise.
(texlive-newverbs)[native-inputs]: Likewise.

Change-Id: I6ba5352b1b1b8ab810da3730b09cb9db61d6429c
Co-authored-by: Simon Tournier <zimon.toutoune@gmail.com>

tests/packages.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012-2023 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012-2024 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 ;;; Copyright © 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
 ;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
@@ -2051,6 +2051,14 @@
    (dummy-package "a"
      (arguments (this-package-native-input "hello")))))
 
+(test-equal "this-package-input, origin"
+  "http://example.org/foo.tar.gz"
+  (origin-uri
+   (package-arguments
+    (dummy-package "a"
+      (inputs (list (dummy-origin (uri "http://example.org/foo.tar.gz"))))
+      (arguments (this-package-input "foo.tar.gz"))))))
+
 (test-eq "modify-inputs, replace"
   coreutils
   ;; Replace an input; notice that the label in unchanged.