[FIXED JENKINS-18074] Avoid clearing AbstractItem.displayName when the new parent ItemGroup is different.

Completed, Successful & Stable using Enum

Copying every time causes overwriting files in the webapp directory, and often causes errors in Windows.
This reverts JENKINS-12647(commit 7ae303f8).

Amends lvotypko’s 33e0df78 to be as careful as bdff4254 + f65da7f9 + 10e9b002 for persistent actions.

Invalid request submission: {json=[Ljava.lang.String;@2c46358e, .crumb=[Ljava.lang.String;@35661457}
Diagnostics added in 21bf5c45.
Failing I think because message.groovy uses f.submit rather than a plain <input type="submit">,
so JSON gets created and then StaplerRequest.getParameter cannot find it.
But if this is the problem then why would it ever work?
Perhaps a timing issue: JavaScript is used to massage the form just prior to submission,
and maybe this only happens sometimes?
Cannot reproduce test failure locally.

This adds an extension point, TestNameTransformer, which is called to transform JUnit test case names.
This is useful for JVM languages like scala which are more flexible than java with identifier naming.
Scala, for example, allows you to write test names between back ticks, and then encodes the name using valid java identifiers.
This extension point would allow a plugin to transform those names back in to readable names when they are displayed on the test result page.