RFR: 8263470: Consolidate copies of getClassBytes in various tests

[Mikhailo Seledtsov]

On Fri, 12 Mar 2021 01:16:18 GMT, Coleen Phillimore <coleenp 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).

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