When the downleveling helper function has been inlined into the
`$localize` call, it is a bit more tricky to parse out the cooked and
raw strings. There was already code to do this but it assumed that
the `cooked` and `raw` items were both arrays.
Sometimes the `raw` array is just a copy of the `cooked` array
via an expression similar to `raw || (raw=tcookedslice(0))`. This
commit changes the `unwrapMessagePartsFromLocalizeCall()`
function to be able to handle such a situation.
Fixes#40702
PR Close#40754
ce44a3d1dc