RFR: Initial sizing refactor

[Y. Srinivas Ramakrishna]

On Fri, 16 Dec 2022 00:36:41 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Some things to highlight here:
> * This change borrows a bit of code from G1 to handle processing of command line arguments used to size the young generation.
> * A (hard coded for now) threshold on the difference between young/old time has been added to reduce resizing churn.
> * The adaptive heuristic doesn't consider the `soft_tail` anymore. `available` is already adjusted for the soft max capacity.
> * `SoftMaxHeapSize` is used to compute the soft max size and max size for the young generation.

Overall I really like these refactorings/changes. I've done a quick overview review and left a few comments/suqestions, but will work through some of the remaining details tomorrow. Thanks!

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PR: https://git.openjdk.org/shenandoah/pull/185