packages: 'package-input-rewriting' has a #:deep? parameter.

* guix/packages.scm (package-input-rewriting): Add #:deep? and pass it
to 'package-mapping'.
[replacement-property]: New variable.
[rewrite]: Check it.
[cut?]: New procedure.
* tests/packages.scm ("package-input-rewriting"): Pass #:deep? #f and
ensure implicit inputs were not rewritten.  Avoid 'eq?' comparisons.
("package-input-rewriting, deep"): New test.
* gnu/packages/guile.scm (package-for-guile-2.0, package-for-guile-3.0):
Pass #:deep? #f.