RFR: JDK-8310814: Clarify the targetName parameter of Lookup::findClass

[Mandy Chung]

This PR updates the spec of `Lookup::findClass` to reflect the current behavior that requires a binary name or a string representing an array class in the form as returned by `Class::getName`.    

`test/jdk/java/lang/invoke/accessClassAndFindClass/TestFindClass.java` already covers the test cases of a nested class and an array class.

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Commit messages:
 - JDK-8310833: Clarify the targetName parameter of Lookup::findClass
 - JDK-8310922: java/lang/Class/forName/ForNameNames.java fails after being added by JDK-8310242

Changes: https://git.openjdk.org/jdk/pull/14668/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14668&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310814
  Stats: 9 lines in 2 files changed: 7 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14668.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14668/head:pull/14668

PR: https://git.openjdk.org/jdk/pull/14668