RFR: 8240908: RetransformClass does not know about MethodParameters attribute

[Alex Menkov]

Changes:
- ClassFileReconstituter is updated to restore "MethodParameters" attribute;
- handling of the attribute in VM_RedefineClasses is moved to be consistent with other code (like local variable table);
- copied ClassTransformer class (from test/jdk/com/sun/jdi/lib/jdb) to /test/lib as it's used by tests from hotspot and jdk (and also by test from Valhalla repo); Will file a follow up issues to updates tests and remove the class from test/jdk/com/sun/jdi/lib/jdb

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Commit messages:
 - JDK-8240908

Changes: https://git.openjdk.java.net/jdk/pull/7180/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7180&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8240908
  Stats: 431 lines in 5 files changed: 411 ins; 15 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7180.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7180/head:pull/7180

PR: https://git.openjdk.java.net/jdk/pull/7180