RFR: 8272808: Update constant collections to use the new immutable collections - leftovers [v2]

[Nir Lisker]

On Fri, 15 Oct 2021 14:24:15 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

>> Replacements of more immutable collections.
>> 
>> One thing I found was that the field `idMap` in `com.sun.java.scene.web.WebViewHelper.WebView` seems unused. I can remove it if that's indeed the case.
>
> Nir Lisker has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Removed unused imports

@johanvos Can you comment on `idMap` in `com.sun.java.scene.web.WebViewHelper.WebView`?

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PR: https://git.openjdk.java.net/jfx/pull/627