RFR: 8255381: com/sun/jdi/EATests.java should not suspend graal threads

[Richard Reingruber]

This fixes a bug in the test test/jdk/com/sun/jdi/EATests.java that caused
timeout failures when graal is enabled.

The fix is to avoid suspending all threads when a breakpoint is reached and then resume
just the main thread again. This pattern was used in the test case
EAMaterializeLocalAtObjectPollReturnReturn. It caused timeouts because graal
threads remained suspended and, running with -Xbatch, the main thread waited
(with timeout) for completion of compile tasks.
The fix was applied to all breakpoints in the test. All explicit suspend calls now apply only
to the main test thread and all explicit resume calls apply to all java threads.

Testing: duration of the test case EAMaterializeLocalAtObjectPollReturnReturn is
reduced from 30s to 10s.

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Commit messages:
 - 8255381: com/sun/jdi/EATests.java should not suspend graal threads

Changes: https://git.openjdk.java.net/jdk/pull/1625/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1625&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255381
  Stats: 91 lines in 2 files changed: 33 ins; 10 del; 48 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1625.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1625/head:pull/1625

PR: https://git.openjdk.java.net/jdk/pull/1625