docs: update popover custom target story

[spmonahan]

Previous Behavior

Previously the example relied on React refs as dependencies to a useEffect() call but these will never trigger the effect. The example still works but when trying to extrapolate from it and target elements that appear after the first render, the example breaks down because the effect will not be triggered.

New Behavior

This example takes advantage of the fact that useMergedRefs() supports functions as refs so we can trigger the effect when the refs are set.

Using setState() was also considered but this will always trigger a re-render, negatively affecting performance so this pattern, while perhaps useful in some cases, is not a good example for best practices documentation. setState() is the approach demonstrated in the positioning docs (link)

The useEffect() could have its dependencies removed so it would be called every render which should allow it to function as needed with less of a performance overhead than the setState() approach. This may be a better approach for documentation.

Related Issue(s)

This PR is motivated by user feedback.

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[fabricteam]

Perf Analysis (@fluentui/react-components)

No significant results to display.

All results

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
Avatar	mount	617	646	5000
Button	mount	310	314	5000
Field	mount	1119	1097	5000
FluentProvider	mount	715	714	5000
FluentProviderWithTheme	mount	78	82	10
FluentProviderWithTheme	virtual-rerender	36	33	10
FluentProviderWithTheme	virtual-rerender-with-unmount	76	71	10
MakeStyles	mount	864	862	50000
Persona	mount	1730	1659	5000
SpinButton	mount	1384	1370	5000
SwatchPicker	mount	1510	1527	5000

[fabricteam]

📊 Bundle size report

✅ No changes found

[fabricteam]

🕵 fluentuiv9 No visual regressions between this PR and main