cabal import parser doesn't support common stanzas

As far as I can tell, the cabal parser for the `guix import` command (https://git.savannah.gnu.org/cgit/guix.git/tree/guix/import/cabal.scm)does not support common stanzas, as specified in the cabal specification (https://cabal.readthedocs.io/en/3.4/cabal-package.html#common-stanzas).

This means that some packages, like "versions" (https://hackage.haskell.org/package/versions-5.0.0/src/versions.cabal)and all depending packages cannot be imported using `guix import hackage versions`:

```

$ guix import hackage versions

Syntax error: unexpected token : common (at line 36, column 0)

Syntax error: unexpected end of input

guix import: error: failed to download cabal file for package 'versions'

```

merge 48700 48701

This issue has been fixed by #48943 and should be closed.

Philip Munksgaard writes:

You can close a bug report by emailing NNN-done@debbugs.gnu.org where

NNN is the bug number.

For the body of the email you can say something like "Closing because

<reason>".