RFR: JDK-8263411: Convert jshell tool to use Stream.toList() [v2]

[Ian Graves]

On Thu, 18 Mar 2021 20:25:14 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> Ian Graves has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Removing most explicit casts and refactoring a Stream use
>
> Overall looks good to me. Please see two comments inline.

Updated mostly in line with @lahodaj 's suggestions. I removed one explicit map-cast and replaced it with an explicit type argument to guide the type checker to the right widening.

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PR: https://git.openjdk.java.net/jdk/pull/2979