With many particle emitters open, perf tanks. Cascade is ticking even if the editor tab is not visible/active, which can cause all sorts of performance issues. Cascade ticks through engine tick, so the only way to properly avoid this is to check for ticking of the viewport widget; added a flag to it to keep track of ticking in the last frame, then checking and clearing that in the Cascade tick function.
#codreview nick.atamas dave.ratti
[CL 2523454 by Olaf Piesche in Main branch]
Editor - Removing some old code that causes crashes in the editor when attempting to click on viewport menu anchors under low framerates, or when the frame rate is articially low, like coming back from the window not being focused. The viewport toolbar no longer attempts to collapse when the frame rate is low, or the window is not focused.
[CL 2436762 by Matthew Griffin in Main branch]
* Moved Slate.h into SlateBasics.h and began shifting less commonly used headers into SlateExtras.h.
* Slate.h now simply includes SlateBasics.h and SlateExtras.h.
* Slate.h includes a deprecated warning now to indicate that SlateBasics.h + specific includes should be used instead.
* Moved dozens of inlined functions using Slate widgets into .cpp files to avoid header dependencies.
* All code samples now include SlateBasics.h and SlateExtras.h so future shifts will not break most those projects, but not trigger the deprecation warning of including Slate.h.
#BUN
[CL 2329610 by Wes Hunt in Main branch]
