Move on{animation,transition}XX event handlers to GlobalEventHandlers

The spec defines these on GlobalEventHandlers, not on Window:
https://drafts.csswg.org/css-animations-1/#interface-globaleventhandlers-idl
https://drafts.csswg.org/css-transitions-1/#interface-globaleventhandlers-idl

Bug: 999894
Change-Id: Idf3d5f9ba44a5cc8045315baa8c204fdc326d5db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1783058
Reviewed-by: Yi Gu <yigu@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696040}