guix build: Move transformation options to (guix transformations).

guix build: Move transformation options to (guix transformations).

* guix/transformations.scm: New file.
* tests/scripts-build.scm: Rename to...
* tests/transformations.scm: ... this.
* Makefile.am (MODULES): Add 'guix/transformations.scm'.
(SCM_TESTS): Adjust to rename.
* guix/scripts/build.scm (numeric-extension?)
(tarball-base-name, <downloaded-file>, download-to-store*)
(compile-downloaded-file, package-with-source)
(transform-package-source, evaluate-replacement-specs)
(transform-package-inputs, transform-package-inputs/graft)
(%not-equal, package-git-url, evaluate-git-replacement-specs)
(transform-package-source-branch, transform-package-source-commit)
(transform-package-source-git-url, package-dependents/spec)
(package-toolchain-rewriting, transform-package-toolchain)
(transform-package-with-debug-info, transform-package-tests)
(%transformations, transformation-procedure, %transformation-options)
(show-transformation-options-help, options->transformation)
(package-transformations): Move to (guix transformations).
* guix/scripts/environment.scm: Adjust accordingly.
* guix/scripts/graph.scm: Likewise.
* guix/scripts/install.scm: Likewise.
* guix/scripts/pack.scm: Likewise.
* guix/scripts/package.scm: Likewise.
* guix/scripts/upgrade.scm: Likewise.
* po/guix/POTFILES.in: Add 'guix/transformations.scm'.