8348033: Tidy Nashorn code

[szegedi]

Over time, a bunch of unused imports, unnecessary local variables, opportunities to lambdify and use better APIs have sprung up. A tidy pass over Nashorn codebase is overdue, still keeping Java 11 as a target (so, not using any 12+ features yet.)

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Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace

Issue

• JDK-8348033: Tidy Nashorn code (Task - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/nashorn.git pull/23/head:pull/23
$ git checkout pull/23

Update a local copy of the PR:
$ git checkout pull/23
$ git pull https://git.openjdk.org/nashorn.git pull/23/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 23

View PR using the GUI difftool:
$ git pr show -t 23

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/nashorn/pull/23.diff

[bridgekeeper]

👋 Welcome back attila! A progress list of the required criteria for merging this PR into main will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[lagergren]

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