RFR: 8263470: Consolidate copies of getClassBytes in various tests

[Coleen Phillimore]

On Fri, 12 Mar 2021 19:35:01 GMT, Mikhailo Seledtsov <mseledtsov at openjdk.org> wrote:

>> See issue for details. This also moves ClassUnloadCommon and ClassWithManyMethodsClassLoader to jdk/lib/test/classloader and puts it in a package with other class loader test utility functions. I left getClassBytes in ClassunloadCommon, because most tests that use it also need to import ClassUnloadCommon.
>> 
>> Tested with tier1-3.
>
> Marked as reviewed by mseledtsov (Committer).

Thanks Harold, Misha and Thomas for the code reviews.

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PR: https://git.openjdk.java.net/jdk/pull/2954