In preparation for gh-29163, this commit revamps
PathMatchingResourcePatternResolverTests as follows.
- organizes tests into @Nested test classes
- reintroduces the @Disabled classpathStarWithPatternOnFileSystem() test
- stops asserting the protocol of Resource URLs, since the protocol is
dependent on the environment -- for example, file: and jar: URLs are
actually resource: URLs within a GraalVM native image
- simplifies implementation of test methods and assertFilenames()
29442d4b7a