RFR: 6899: Upgrade core to 8 [v2]

[Guru Hb]

On Sun, 4 Oct 2020 19:25:45 GMT, Marcus Hirt <hirt at openjdk.org> wrote:

>> For some reason the Eclipse compiler fails some type inferences when switching to JDK 8, so had to add some
>> (unnecessary) casts. (Also set JDK 11 as required for running the application builds.)
>
> Marcus Hirt has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Formatting

Verified on Mac OS X and Linux.
Please update copyright year for JfrLoaderToolkit.java , Rest of the changed looks good to me.

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Marked as reviewed by ghb (Reviewer).

PR: https://git.openjdk.java.net/jmc/pull/120