RFR: 8282076: Merge some debug agent changes from the loom repo

[Alex Menkov]

On Thu, 17 Feb 2022 21:32:14 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> There are some minor debug agent changes in the loom repo that are not virtual thread specific, and I would like to merge them into the jdk repo. This will make the future real merge of loom into jdk a bit cleaner. 
> 
> The biggest change is moving some code into the new filterAndHandleEvent() function. However, there are no logic changes. It's the same code, just moved into its own function.
> 
> In handleMethodEnterEvent() I reworked some confusing logic and also the comment that goes with it, but it should be functionally the same.
> 
> ### Tests:
> - [x] vmTestbase/nsk/jdb
> - [x] vmTestbase/nsk/jdi
> - [x] vmTestbase/nsk/jdwp
> - [x] serviceability/jdwp
> - [x] jdk/com/sun/jdi

Marked as reviewed by amenkov (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/7524