RFR: 6965: Thirdparty licenses missing in core, Maven plugins version update

[Guru Hb]

Fix contails : 
1 "THIRD_PARTY_LICENSES.txt" (new file) contain license attributes of owasp java encoder and lz4-java.
2. "LICENSE.TXT" should be contained in the root directory (inside jar) instead of "rootdir/license/Licenses.txt" (which was earlier fixed in JMC-6951" 
3. Maven build time plugins version update for : 
 [core] update maven dependent plugin with latest version : 
   org.apache.maven.plugins:maven-jar-plugin:3.2.0 (old : 3.1.0)
   org.apache.maven.plugins:maven-resources-plugin:3.2.0 (old : 3.0.2) 
   org.apache.maven.plugins:maven-source-plugin:3.2.1 (old: 3.0.2) 
   org.apache.maven.plugins:maven-javadoc-plugin: 3.2.0 (old : 3.0.2) 
 [jmc] 
   org.commonjava.maven.plugins:directory-maven-plugin:0.3.1 (old : 0.2)
   org.apache.maven.plugins:maven-resource-plugin:3.2.0 (old : 3.0.2)
junit:junit:4.13.1 (old : 4.12)

4. Fixed javadoc error (Invalid parameter 'the"  in IPoolFactory.java) after upgrading javadoc-plugin with 3.2.0
5. [Core] Fixed Warning "'build.plugins.plugin.version' for org.apache.maven.plugins:maven-jar-plugin is missing" in test modules : missing <version> value in the test pom.xml

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Commit messages:
 - 6965: Thirdparty licenses missing in core, Maven plugins version update

Changes: https://git.openjdk.java.net/jmc/pull/154/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=154&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6965
  Stats: 343 lines in 14 files changed: 319 ins; 3 del; 21 mod
  Patch: https://git.openjdk.java.net/jmc/pull/154.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/154/head:pull/154

PR: https://git.openjdk.java.net/jmc/pull/154