RFR: 8288623: Move Continuation classes out of javaClasses.hpp [v3]

[Ioi Lam]

On Fri, 17 Jun 2022 20:18:56 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fixed include guard macro and copyright year
>
> I've talked to Ioi and Coleen about whether `javaClasses` or `continuations` should be considered as the most relevant subsystem. Their take is that `continuations` is. I'm warming up to that thought, but I think I'd then would prefer if continuationsJavaClasses.hpp etc. get moved to where the other continuation files are, in the runtime/ directory.

Thanks to @stefank and @coleenp for the review.

- Passes our CI tier1 and build-tier5.
- GHA linux-x86 errors are unrelated to my changes.

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PR: https://git.openjdk.org/jdk/pull/9191