Fix MethodUtils.invokeMethod on instances of non-public classes

[lenamonj]

getMatchingAccessibleMethod has an exact-signature fast path, added in #1427, that returns the Method declared on the receiver's own class without the accessible-declaration lookup the search path does. When that class is not public, which is every JDK collection factory result (Collections.emptyList(), Arrays.asList(), Collections.emptyMap()), invokeMethod throws IllegalAccessException although a public declaration exists on the interface.

The fast path now re-resolves the hit through getAccessibleMethod and keeps the original only when no public declaration exists, so a package-private class that setAccessible can open behaves as before.

Tests: four in MethodUtilsTest, red on master (three failures, one error) and green with the change. Default Maven goal green.

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