[eacsl] Add functions to strip and add casts

Contrary to the function `Cil.stripCasts`, the function
`Misc.strip_casts` returns the list of removed casts.

Contrary to the function `Cil.mkCast`, the function `Misc.add_casts` is
able to successively add a list of cast like the one returned by
`Misc.strip_casts`.