test: add test for pasting over mentions #388

Job	Run time
e2e-collab-linux (18.18.0, chromium)	4m 20s
e2e-collab-mac (18.18.0, chromium)	4m 15s
e2e-linux (18.18.0, chromium, rich-text, modern-events)	3m 39s
e2e-collab-linux (18.18.0, firefox)	6m 43s
e2e-collab-mac (18.18.0, firefox)	30m 34s
e2e-collab-windows (18.18.0, chromium)	6m 30s
e2e-linux (18.18.0, chromium, plain-text, modern-events)	2m 15s
e2e-collab-mac (18.18.0, webkit)	6m 24s
e2e-collab-windows (18.18.0, firefox)	19m 34s
e2e-linux (18.18.0, firefox, rich-text, modern-events)	6m 0s
e2e-mac (18.18.0, chromium, rich-text, modern-events)	3m 11s
e2e-linux (18.18.0, firefox, plain-text, modern-events)	3m 58s
e2e-mac (18.18.0, chromium, plain-text, modern-events)	2m 7s
e2e-windows (18.18.0, chromium, rich-text, legacy-events)	6m 46s
e2e-mac (18.18.0, firefox, rich-text, modern-events)	29m 37s
e2e-windows (18.18.0, chromium, rich-text, modern-events)	5m 7s
e2e-mac (18.18.0, firefox, plain-text, modern-events)	29m 3s
e2e-windows (18.18.0, chromium, plain-text, legacy-events)	3m 39s
e2e-mac (18.18.0, webkit, rich-text, modern-events)	5m 6s
e2e-windows (18.18.0, chromium, plain-text, modern-events)	3m 22s
e2e-mac (18.18.0, webkit, plain-text, modern-events)	3m 12s
e2e-windows (18.18.0, firefox, rich-text, modern-events)	17m 36s
e2e-windows (18.18.0, firefox, plain-text, modern-events)	13m 58s
	3h 36m 56s

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