Bugfix for Delphi IDE explorer in Delphi 10.3

In December 2018 I found out that some of the functionality in my Delhi IDE explorer was broken in Delphi 10.3, namely the function to select the current active control or automatically follow the focus. The reason was that the IDE now used the Screen.ActiveControlChanged event itself, disabling it for to my plugin.

Today I finally found a way to fix it, so the current source code will work with Delphi 10.3 (all three releases).