RFR: 8305785: Avoid redundant HashMap.containsKey call in java.util.regex

[Sergey Tsypanov]

On Mon, 3 Apr 2023 16:58:15 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

> `Pattern.namedGroups` and `Matcher.namedGroups` contains only non-null values. It means instead of separate `containsKey`+`get` calls, we can use single `HashMap.get` call and then compare result with null.
> Result code is a bit simpler and faster.

Marked as reviewed by stsypanov (Author).

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PR Review: https://git.openjdk.org/jdk/pull/13303#pullrequestreview-1386780737