Clean up JavaLangReflectAccess

JavaLangReflectAccess exposes a lot of unnecessary APIs: many getters are just for creating a new constructor with same values, which can be done in j.l.reflect and exposed through a single API. Some other APIs, like leafCopy, can be converted to getRoot().copy as well. In principle, we should reduce usages of SharedSecrets, using them only as the last resort.