RFR: 8281631: HashMap copy constructor and putAll can over-allocate table [v21]

[liach]

On Sun, 20 Feb 2022 19:41:22 GMT, XenoAmess <duke at openjdk.java.net> wrote:

>> In fact, if we do worry about the performance of adding from maps, calling `map.forEach(this::put);` would be a better alternative both in concurrency (as the concurrent map itself takes charage) and object allocation-wise (no allocation of immutable entry objects), but that belongs to another issue.
>
> @liach Hi. please have a look at the latest commit.
> do you think it be better now?

Oops, didn't notice there was this helpful `init` method. Does look much more straightforward now.

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PR: https://git.openjdk.java.net/jdk/pull/7431