proto(dropdown at mentions): improvement to highlight first item when open

[kolaps33]

Description of changes

During working on bug
microsoft/fluent-ui-react#1193

I recognized I can do prototype improvement. :)

Focus areas to test

type "@" to at mention proto
Expected: first item in dropdown is highlighted

Microsoft Reviewers: Open in CodeFlow

[size-auditor]

Asset size changes

Size Auditor did not detect a change in bundle size for any component!

Baseline commit: 3f7fedb89433048b03009065460e754079adb050 (build)

[msft-github-bot]

Perf Analysis

No significant results to display.

All results

Scenario	Master Ticks	PR Ticks	Iterations	Status
BaseButton	823	809	5000
Checkbox	1627	1586	5000
CheckboxBase	1255	1285	5000
ChoiceGroup	4851	4920	5000
ComboBox	906	941	1000
CommandBar	7522	7559	1000
ContextualMenu	14461	14330	1000
DefaultButton	1037	1039	5000
DetailsRow	3388	3387	5000
DetailsRow (fast icons)	3354	3389	5000
DetailsRow without styles	3116	3255	5000
Dialog	1467	1463	1000
DocumentCardTitle with truncation	1598	1658	1000
Dropdown	2335	2257	5000
FocusZone	1582	1560	5000
IconButton	1661	1636	5000
Label	292	272	5000
Link	444	430	5000
MenuButton	1348	1398	5000
Nav	3133	3135	1000
Panel	1391	1495	1000
Persona	813	800	1000
Pivot	1273	1277	1000
PrimaryButton	1175	1196	5000
SearchBox	1213	1205	5000
Slider	1450	1460	5000
Spinner	386	378	5000
SplitButton	3023	3040	5000
Stack	455	458	5000
Stack with Intrinsic children	1111	1142	5000
Stack with Text children	3971	3980	5000
TagPicker	2660	2656	5000
Text	346	358	5000
TextField	1352	1347	5000
Toggle	842	853	5000
button	59	68	5000

Perf Analysis (Fluent)

Perf comparison

Status	Scenario	Fluent TPI	Fabric TPI	Ratio	Iterations	Ticks
🎯	Avatar.Fluent	0.47	0.47	1:1	2000	940
🦄	Button.Fluent	0.09	0.18	0.5:1	5000	467
🔧	Checkbox.Fluent	0.67	0.35	1.91:1	1000	666
🔧	Dialog.Fluent	0.36	0.2	1.8:1	5000	1778
🔧	Dropdown.Fluent	3.4	0.43	7.91:1	1000	3396
🔧	Icon.Fluent	0.14	0.05	2.8:1	5000	690
🦄	Image.Fluent	0.07	0.11	0.64:1	5000	359
🔧	Slider.Fluent	1.45	0.34	4.26:1	1000	1446
🔧	Text.Fluent	0.07	0.02	3.5:1	5000	325
🦄	Tooltip.Fluent	0.09	17.71	0.01:1	5000	465

🔧 Needs work     🎯 On target     🦄 Amazing

Perf tests with no regressions

Scenario	Current PR Ticks	Baseline Ticks	Ratio
DividerMinimalPerf.default	846	720	1.18:1
ListNestedPerf.default	950	869	1.09:1
ToolbarMinimalPerf.default	1048	966	1.08:1
AvatarMinimalPerf.default	525	491	1.07:1
ButtonSlotsPerf.default	611	575	1.06:1
CardMinimalPerf.default	573	539	1.06:1
TreeMinimalPerf.default	1225	1160	1.06:1
VideoMinimalPerf.default	605	573	1.06:1
ChatMinimalPerf.default	627	597	1.05:1
StatusMinimalPerf.default	656	622	1.05:1
CheckboxMinimalPerf.default	3005	2886	1.04:1
FormMinimalPerf.default	744	713	1.04:1
GridMinimalPerf.default	686	657	1.04:1
InputMinimalPerf.default	1004	963	1.04:1
LabelMinimalPerf.default	402	387	1.04:1
LayoutMinimalPerf.default	584	560	1.04:1
ProviderMergeThemesPerf.default	1693	1626	1.04:1
TreeWith60ListItems.default	232	223	1.04:1
Checkbox.Fluent	666	643	1.04:1
Icon.Fluent	690	661	1.04:1
AttachmentMinimalPerf.default	146	142	1.03:1
HierarchicalTreeMinimalPerf.default	977	953	1.03:1
TooltipMinimalPerf.default	728	706	1.03:1
Image.Fluent	359	347	1.03:1
Text.Fluent	325	316	1.03:1
MenuMinimalPerf.default	1816	1789	1.02:1
MenuButtonMinimalPerf.default	1578	1551	1.02:1
SegmentMinimalPerf.default	927	913	1.02:1
Tooltip.Fluent	465	454	1.02:1
ButtonMinimalPerf.default	151	150	1.01:1
ChatDuplicateMessagesPerf.default	423	420	1.01:1
ChatWithPopoverPerf.default	602	599	1.01:1
DropdownManyItemsPerf.default	1353	1346	1.01:1
ItemLayoutMinimalPerf.default	1607	1588	1.01:1
PortalMinimalPerf.default	307	303	1.01:1
ReactionMinimalPerf.default	1897	1873	1.01:1
SplitButtonMinimalPerf.default	3351	3319	1.01:1
Dropdown.Fluent	3396	3359	1.01:1
Slider.Fluent	1446	1428	1.01:1
DropdownMinimalPerf.default	3295	3290	1:1
HeaderMinimalPerf.default	490	490	1:1
HeaderSlotsPerf.default	1471	1465	1:1
PopupMinimalPerf.default	264	263	1:1
RefMinimalPerf.default	203	204	1:1
Avatar.Fluent	940	940	1:1
Dialog.Fluent	1778	1786	1:1
BoxMinimalPerf.default	315	319	0.99:1
ListMinimalPerf.default	475	479	0.99:1
LoaderMinimalPerf.default	760	764	0.99:1
RadioGroupMinimalPerf.default	545	552	0.99:1
SliderMinimalPerf.default	1395	1405	0.99:1
IconMinimalPerf.default	663	673	0.99:1
TableMinimalPerf.default	530	533	0.99:1
TextMinimalPerf.default	338	340	0.99:1
TextAreaMinimalPerf.default	460	464	0.99:1
AttachmentSlotsPerf.default	1142	1161	0.98:1
CarouselMinimalPerf.default	581	591	0.98:1
ImageMinimalPerf.default	348	355	0.98:1
ListCommonPerf.default	966	988	0.98:1
ListWith60ListItems.default	1122	1147	0.98:1
EmbedMinimalPerf.default	4263	4375	0.97:1
AlertMinimalPerf.default	271	281	0.96:1
FlexMinimalPerf.default	279	291	0.96:1
CustomToolbarPrototype.default	3660	3812	0.96:1
Button.Fluent	467	484	0.96:1
ProviderMinimalPerf.default	669	703	0.95:1
AnimationMinimalPerf.default	630	670	0.94:1
DialogMinimalPerf.default	1696	1805	0.94:1
AccordionMinimalPerf.default	231	251	0.92:1

[DustyTheBot]

	Warnings
⚠️	There are no updates provided to CHANGELOG. Ensure there are no publicly visible changes introduced by this PR.

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[silviuaavram]

just a small comment