update src/stubber/tools/manifestfile.py from Micropython repo

[Josverl]

Update needed to be able to process newer manifests in get-frozen

tools/manifestfile.py: Change library search to use a list of paths.
This commit changes how library packages are searched for when a manifest
file is loaded: there is now simply a list of library paths that is
searched in order for the given package. This list defaults to the
main directories in micropython-lib, but can be added to -- either appended
or prepended -- by using add_library()

micropython/micropython@micropython:2bdaa1b...micropython:8cbae12