Repainting decorations on editor switch is too slow

[memeplex]

Take a look at this screencast https://github.com/microsoft/vscode/issues/136241#issuecomment-956604726

I haven't looked at the code but I think this is due to throttling decoration on editor activation. I've seen this in other extensions, for example here is a patch I wrote for foam https://github.com/foambubble/foam/pull/811. There is a "canonical" example in vscode site that adds delay to both cases: changes in a document and change of editor. Throttling the first one is ok but the example is misleading regarding the second one. I've reported a more general issue to optimize the way decorations work (https://github.com/microsoft/vscode/issues/136241) but in any case removing the delay for the editor activation case is usually a very easy change.