Fix tests and example code to run under Pharo 14

[belaroesener]

Many tests failed, and the first code example in the README did not work in Pharo 14. These changes fix both.

Summary of changes:

• OSSUnixSubprocess >> #defaultEncoding: Use OSPlatform instead of OSEnvironment to retrieve the default encoding.
• OSSUnixSubprocessTest >> #withNonAsciiDirectoryDo:: Use UUID class >> #new instead of UUIDGenerator class >> #next, as the latter does not exist anymore.

[belaroesener]

When running the tests, a lot of automatic code changes are made (because of Object >> #deprecated:transformWith:), should I create a commit with these changes?