Ability to pause particle simulation in the editor

[Calinou]

It should be possible to pause particle simulation while in the editor, to decrease CPU/GPU usage while using the 2D or 3D viewports (no refreshing has to be done when nothing is moving in the viewport). This could be done using a single checkbox to toggle simulation of all particles; it's probably a good idea that non-explosive particles (at least) stay visible while they are paused.

[KoBeWi]

Feature and improvement proposals for the Godot Engine are now being discussed and reviewed in a dedicated Godot Improvement Proposals (GIP) (godotengine/godot-proposals) issue tracker. The GIP tracker has a detailed issue template designed so that proposals include all the relevant information to start a productive discussion and help the community assess the validity of the proposal for the engine.

The main (godotengine/godot) tracker is now solely dedicated to bug reports and Pull Requests, enabling contributors to have a better focus on bug fixing work. Therefore, we are now closing all older feature proposals on the main issue tracker.

If you are interested in this feature proposal, please open a new proposal on the GIP tracker following the given issue template (after checking that it doesn't exist already). Be sure to reference this closed issue if it includes any relevant discussion (which you are also encouraged to summarize in the new proposal). Thanks in advance!

:v