[Security Solution] Editing the Action Message of a detection rule results in cursor jumping to end

[spong]

Reported in 8.5, when editing a Detection Rule's Action Message, the cursor will jump to the end of the text area, preventing the user from making in-line edits.

Steps to reproduce:

1. Edit a Detection Rule
2. Go to Actions, then select a frequency and connector
3. Give focus to the Message text area, add a chunk of text, move the cursor up a few lines and then start typing again
4. Notice that after the first typed character the remaining text is appended to the end instead of where the cursor was.

Looks like this was initially introduced in 8.5 as part of this fix for managing param validation.

kibana/x-pack/plugins/security_solution/public/detections/components/rules/rule_actions_field/index.tsx

Lines 99 to 116 in ff6024d

	// validation is not triggered correctly when actions params updated (more details in https://github.com/elastic/kibana/issues/142217)
	// wrapping field.setValue in setTimeout fixes the issue above
	// and triggers validation after params have been updated
	setTimeout(
	() =>
	field.setValue((prevValue: RuleAction[]) => {
	const updatedActions = [...prevValue];
	updatedActions[index] = {
	...updatedActions[index],
	params: {
	...updatedActions[index].params,
	[key]: value,
	},
	};
	return updatedActions;
	}),
	0
	);

If you remove the setTimeout the Message EuiTextArea begins to function as expected. Probable conflict with onChange/onFocus set on the underlying EuiTextArea:

kibana/x-pack/plugins/triggers_actions_ui/public/application/components/text_area_with_message_variables.tsx

Lines 75 to 78 in 4f3e554

	onChange={(e: React.ChangeEvent<HTMLTextAreaElement>) => onChangeWithMessageVariable(e)}
	onFocus={(e: React.FocusEvent<HTMLTextAreaElement>) => {
	setCurrentTextElement(e.target);
	}}

---

Edit:

Looks like there's some excessive re-render going on here as well...

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

Pinging @elastic/security-detections-response (Team:Detections and Resp)