Selecting a node triggers too many gui (JMeterGUIComponent) updates / configuration

**benoit.wiart** ([Bug 51822](https://bz.apache.org/bugzilla//show_bug.cgi?id=51822&redirect=false)):
For a test plan with 2 samplers
Sampler A
Sampler B

Switching from A to B will trigger too many gui (JMeterGUIComponent) updates / configuration
Precisely :
1 JMeterGUIComponent#modifyTestElement for A
3 JMeterGUIComponent#modifyTestElement for B
4 JMeterGUIComponent#configure for B
3 JMeterGUIComponent#clearGui for B

The root cause is GuiPackage #getCurrentGui being call 3 times
EditCommand : 2 times
MenuFactory#addFileMenu : 1

For components which do costly computation in JMeterGUIComponent#configure (eg : WebServiceSamplerGui) this bug introduce a lag the jmeter gui usage.
If the component displays a popup in JMeterGUIComponent#configure, it will be displayed 3 times…

I think we should review the way GuiPackage #getCurrentGui is used and at least rename it because this method is doing much more than getting the current gui.

The first patch does not correct the root cause but save 1 invocation.

Votes in Bugzilla: 1
OS: All

Blocks:
* https://github.com/apache/jmeter/issues/2542