RFR: 8293036: x86_64: Move Continuation-related stub methods to MacroAssembler

[Vladimir Ivanov]

On Mon, 29 Aug 2022 17:17:22 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> Move Continuation-related methods from `stubGenerator_x86_64.cpp` under `MacroAssembler`.
> 
> Testing: hs-tier1 - hs-tier2

Thanks for the review, Dean.

> It looks good, but I'm curious, what's the motivation?

It's a worthwhile cleanup per se, but it'll also benefit forthcoming cleanups in  `stubGenerator_x86_64.cpp`.

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PR: https://git.openjdk.org/jdk/pull/10066