RFR: 8282076: Merge some debug agent changes from the loom repo [v2]

[Chris Plummer]

> 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

Chris Plummer has updated the pull request incrementally with one additional commit since the last revision:

  Update copyright

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7524/files
  - new: https://git.openjdk.java.net/jdk/pull/7524/files/623d838b..52c614f5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7524&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7524&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7524.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7524/head:pull/7524

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