bitbake: tinfoil: add a parse_recipe_file function

bitbake: tinfoil: add a parse_recipe_file function

Parsing a recipe is such a common task for tinfoil-using scripts, and is
a little awkward to do properly, so add an API function to do it. This
should also isolate scripts a little from future changes to the internal
code. The first user of this will be the OpenEmbedded layer index update
script.

Part of the fix for [YOCTO #10192].

(Bitbake rev: 39780b1ccbd76579db0fc6fb9369c848a3bafa9d)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>