RFR: 7951: Factor out commonly used test helper classes from org.openjdk.jmc.common.test into dedicated test library module [v2]

[Christoph Langer]

> Triggered by an issue in project core/tests/org.openjdk.jmc.common.test, I came up with a little refactoring.
> 
> So, org.openjdk.jmc.common.test is somewhat of a hybrid project. It contains both, some common test scaffolding classes plus some actual tests for the org.openjdk.jmc.common module.
> 
> According to our special setup, which is not really like what maven would expect, we have all sources, also for the tests in the src/main/java folder. With a little tweak,
> that is specifying <testSourceDirectory>${project.basedir}/src/main/java</testSourceDirectory> in the pom.xml, we can direct maven to consume the tests from there instead
> of the usually expected src/test/java subfolder. However, when updating the eclipse project configuration from that pom.xml, the project would not export the test helper
> classes to other modules within eclipse any more.
> 
> I'm hereby factoring out the test helper classes into a new module called core/tests/org.openjdk.jmc.testlib. This module will then only serve as a test helper library but
> not contain any actual tests.
> 
> Furthermore I include some other cleanups in project and manifest files, e.g. removal of .settings files which are .gitignored because they would be generated when importing
> the JMC projects into Eclipse.

Christoph Langer has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - Merge branch 'master' into JMC-7951
 - JMC-7951

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Changes: https://git.openjdk.org/jmc/pull/451/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=451&range=01
  Stats: 924 lines in 102 files changed: 195 ins; 368 del; 361 mod
  Patch: https://git.openjdk.org/jmc/pull/451.diff
  Fetch: git fetch https://git.openjdk.org/jmc pull/451/head:pull/451

PR: https://git.openjdk.org/jmc/pull/451