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()

https://github.com/micropython/micropython/compare/micropython:2bdaa1b...micropython:8cbae12