RFR 7902706: IntelliJ jtreg plugin crashes because of removal of deprecated icon

[Maurizio Cimadamore]

Hi,
this is a path that fixes the crash in the intellij jtreg plugin which 
started to occur in the latest version 2020.1.

http://cr.openjdk.java.net/~mcimadamore/7902706/webrev/

This patch is based on some work submitted few weeks ago by John Rhee 
[1]; I sprinkled the usual reflective goop on top to make sure that the 
plugin keeps working against old versions too (as the new Target icon is 
only defined for 2019.x).

I've also added an overload for a method whose implementation is 
deprecated, namely ConfigurationFactory::getId; this should keep things 
from breaking in the medium run.

As a general note, I see that the IDE is giving quite a bit of warning 
around the plugin code - in many instances IntelliJ is trying to move 
towards a lazier/more declarative way to register listener to events 
[2]. But I think a point will come in which we won't be able to evolve 
the plugin in a compatible way - so at some point in the future we 
should probably start thinking about dropping support for older version 
and start using 2019 as base.

Cheers
Maurizio


[1] - https://mail.openjdk.java.net/pipermail/jtreg-dev/2020-May/000826.html
[2] - 
https://www.jetbrains.org/intellij/sdk/docs/basics/plugin_structure/plugin_listeners.html