fix: Making Stack properly render non-ReactElement children

[khmakoto]

PR Description

PR #25397 introduced a way to scope the Stack's child selectors so they wouldn't be as expensive for performance when recalculating styles. However, it seems that, in the process, we restricted Stack to work only with children that are React elements. This PR fixes the issue so that Stack works with any element (with the same restrictions to using enableScopedSelectors still in place).

Related Issue(s)

Fixes #25653

[size-auditor]

Asset size changes

Project	Bundle	Baseline Size	New Size	Difference
office-ui-fabric-react	fluentui-react-TeachingBubble	193.692 kB	193.689 kB	-3 bytes
office-ui-fabric-react	fluentui-react-Stack	40.056 kB	40.053 kB	-3 bytes

 Over Tolerance (1024 B)  Over Baseline  Below Baseline  New   Removed 1 kB = 1000 B

Baseline commit: 4f5eec8081eed87fce6e8c4a071fb48e37629d1c (build)

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

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Latest deployment of this branch, based on commit 5efad2b:

Sandbox	Source
@fluentui/react 8 starter	Configuration
@fluentui/react-components 9 starter	Configuration

[fabricteam]

📊 Bundle size report

_{🤖 This report was generated against 4f5eec8081eed87fce6e8c4a071fb48e37629d1c}

[fabricteam]

Perf Analysis (@fluentui/react)

No significant results to display.

All results

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
BaseButton	mount	1417	1394	5000
Breadcrumb	mount	3443	3495	1000
Checkbox	mount	3148	3149	5000
CheckboxBase	mount	2839	2803	5000
ChoiceGroup	mount	5277	5261	5000
ComboBox	mount	1475	1510	1000
CommandBar	mount	11398	11212	1000
ContextualMenu	mount	12941	13012	1000
DefaultButton	mount	1640	1667	5000
DetailsRow	mount	4269	4286	5000
DetailsRowFast	mount	4394	4306	5000
DetailsRowNoStyles	mount	4210	4177	5000
Dialog	mount	3668	3721	1000
DocumentCardTitle	mount	686	694	1000
Dropdown	mount	3847	3769	5000
FocusTrapZone	mount	2355	2381	5000
FocusZone	mount	2353	2379	5000
GroupedList	mount	2243	2557	2
GroupedList	virtual-rerender	1334	1317	2
GroupedList	virtual-rerender-with-unmount	1921	1972	2
GroupedListV2	mount	662	680	2
GroupedListV2	virtual-rerender	649	641	2
GroupedListV2	virtual-rerender-with-unmount	654	681	2
IconButton	mount	2336	2306	5000
Label	mount	864	861	5000
Layer	mount	5150	5087	5000
Link	mount	989	988	5000
MenuButton	mount	1954	2016	5000
MessageBar	mount	2594	2741	5000
Nav	mount	3957	3860	1000
OverflowSet	mount	1601	1597	5000
Panel	mount	2994	3025	1000
Persona	mount	1488	1509	1000
Pivot	mount	1951	1948	1000
PrimaryButton	mount	1818	1847	5000
Rating	mount	8348	8311	5000
SearchBox	mount	1771	1813	5000
Shimmer	mount	3352	3472	5000
Slider	mount	2439	2476	5000
SpinButton	mount	5519	5567	5000
Spinner	mount	939	957	5000
SplitButton	mount	3758	3721	5000
Stack	mount	968	1010	5000
StackWithIntrinsicChildren	mount	2843	2829	5000
StackWithTextChildren	mount	5799	5836	5000
SwatchColorPicker	mount	13294	12341	5000
TagPicker	mount	3070	3115	5000
TeachingBubble	mount	98145	98744	5000
Text	mount	928	939	5000
TextField	mount	1866	1902	5000
ThemeProvider	mount	1842	1834	5000
ThemeProvider	virtual-rerender	1269	1269	5000
ThemeProvider	virtual-rerender-with-unmount	2560	2602	5000
Toggle	mount	1309	1282	5000
buttonNative	mount	651	642	5000

[khmakoto]

/azp run

[azure-pipelines]

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