docs(Dropdown): update best practice if loadingMessage prop is used

[kolaps33]

Pull request checklist

• Addresses an existing issue: Fixes #0000
• Include a change request file using $ yarn change

Description of changes

adding accessibility recommendation into best practices section

[msft-github-bot]

Perf Analysis

No significant results to display.

All results

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
BaseButton	mount	808	917	5000
ButtonNext	mount	364	375	5000
Checkbox	mount	1457	1486	5000
CheckboxBase	mount	1242	1220	5000
CheckboxNext	mount	1519	1485	5000
ChoiceGroup	mount	5162	4493	5000
ComboBox	mount	904	993	1000
CommandBar	mount	6667	7234	1000
ContextualMenu	mount	11583	11321	1000
DefaultButton	mount	998	987	5000
DetailsRow	mount	3175	3260	5000
DetailsRowFast	mount	3480	3212	5000
DetailsRowNoStyles	mount	3441	3319	5000
Dialog	mount	1344	1423	1000
DocumentCardTitle	mount	1575	1526	1000
Dropdown	mount	2347	2240	5000
FocusZone	mount	1503	1544	5000
IconButton	mount	1587	1590	5000
Label	mount	294	300	5000
Link	mount	485	470	5000
LinkNext	mount	518	550	5000
MenuButton	mount	1487	1516	5000
Nav	mount	3151	3337	1000
Panel	mount	1426	1422	1000
Persona	mount	775	786	1000
Pivot	mount	1386	1406	1000
PivotNext	mount	1249	1218	1000
PrimaryButton	mount	1096	1131	5000
SearchBox	mount	1173	1373	5000
Slider	mount	1613	1368	5000
SliderNext	mount	2007	1946	5000
Spinner	mount	429	449	5000
SplitButton	mount	2813	3022	5000
Stack	mount	463	470	5000
StackWithIntrinsicChildren	mount	1704	1703	5000
StackWithTextChildren	mount	4544	4592	5000
TagPicker	mount	2573	2441	5000
Text	mount	448	434	5000
TextField	mount	1496	1435	5000
ThemeProvider	mount	2478	2721	5000
ThemeProvider	virtual-rerender	474	529	5000
Toggle	mount	797	827	5000
ToggleNext	mount	794	801	5000
button	mount	95	101	5000

Perf Analysis (Fluent)

Perf comparison

Status	Scenario	Fluent TPI	Fabric TPI	Ratio	Iterations	Ticks
🎯	Avatar.Fluent	0.41	0.42	0.98:1	2000	816
🦄	Button.Fluent	0.1	0.17	0.59:1	5000	492
🔧	Checkbox.Fluent	0.57	0.35	1.63:1	1000	575
🦄	Dialog.Fluent	0.15	0.22	0.68:1	5000	757
🔧	Dropdown.Fluent	3.25	0.44	7.39:1	1000	3246
🔧	Icon.Fluent	0.15	0.05	3:1	5000	729
🦄	Image.Fluent	0.06	0.09	0.67:1	5000	321
🔧	Slider.Fluent	1.34	0.32	4.19:1	1000	1341
🔧	Text.Fluent	0.06	0.02	3:1	5000	307
🦄	Tooltip.Fluent	0.08	14.08	0.01:1	5000	399

🔧 Needs work     🎯 On target     🦄 Amazing

Perf tests with no regressions

Scenario	Current PR Ticks	Baseline Ticks	Ratio
DropdownMinimalPerf.default	3337	2834	1.18:1
Icon.Fluent	729	646	1.13:1
IconMinimalPerf.default	626	561	1.12:1
FlexMinimalPerf.default	274	250	1.1:1
ProviderMergeThemesPerf.default	1962	1790	1.1:1
ButtonMinimalPerf.default	156	143	1.09:1
FormMinimalPerf.default	364	338	1.08:1
HierarchicalTreeMinimalPerf.default	389	359	1.08:1
TextAreaMinimalPerf.default	508	474	1.07:1
GridMinimalPerf.default	649	615	1.06:1
ChatWithPopoverPerf.default	408	387	1.05:1
ImageMinimalPerf.default	342	325	1.05:1
AccordionMinimalPerf.default	133	128	1.04:1
CardMinimalPerf.default	499	478	1.04:1
ChatMinimalPerf.default	536	517	1.04:1
Avatar.Fluent	816	786	1.04:1
ChatDuplicateMessagesPerf.default	376	366	1.03:1
DividerMinimalPerf.default	367	355	1.03:1
DropdownManyItemsPerf.default	1378	1334	1.03:1
HeaderSlotsPerf.default	718	694	1.03:1
LabelMinimalPerf.default	382	372	1.03:1
ProviderMinimalPerf.default	747	722	1.03:1
CarouselMinimalPerf.default	392	385	1.02:1
DialogMinimalPerf.default	734	717	1.02:1
ListMinimalPerf.default	437	430	1.02:1
StatusMinimalPerf.default	630	616	1.02:1
TableMinimalPerf.default	353	345	1.02:1
TreeMinimalPerf.default	897	882	1.02:1
Dialog.Fluent	757	742	1.02:1
Text.Fluent	307	302	1.02:1
HeaderMinimalPerf.default	314	312	1.01:1
ItemLayoutMinimalPerf.default	1176	1162	1.01:1
ListWith60ListItems.default	1148	1141	1.01:1
MenuButtonMinimalPerf.default	1324	1307	1.01:1
PopupMinimalPerf.default	262	259	1.01:1
VideoMinimalPerf.default	546	540	1.01:1
AnimationMinimalPerf.default	321	320	1:1
EmbedMinimalPerf.default	1687	1686	1:1
Dropdown.Fluent	3246	3255	1:1
ButtonSlotsPerf.default	528	535	0.99:1
LayoutMinimalPerf.default	347	350	0.99:1
RefMinimalPerf.default	169	170	0.99:1
Slider.Fluent	1341	1355	0.99:1
AttachmentMinimalPerf.default	121	124	0.98:1
AttachmentSlotsPerf.default	1003	1020	0.98:1
AvatarMinimalPerf.default	433	441	0.98:1
BoxMinimalPerf.default	301	307	0.98:1
ListCommonPerf.default	834	849	0.98:1
TooltipMinimalPerf.default	729	744	0.98:1
ListNestedPerf.default	747	771	0.97:1
LoaderMinimalPerf.default	706	725	0.97:1
RadioGroupMinimalPerf.default	372	385	0.97:1
SliderMinimalPerf.default	1345	1383	0.97:1
TextMinimalPerf.default	320	331	0.97:1
Image.Fluent	321	331	0.97:1
ReactionMinimalPerf.default	340	353	0.96:1
SegmentMinimalPerf.default	302	315	0.96:1
SplitButtonMinimalPerf.default	3124	3253	0.96:1
Checkbox.Fluent	575	600	0.96:1
InputMinimalPerf.default	887	932	0.95:1
Tooltip.Fluent	399	419	0.95:1
MenuMinimalPerf.default	822	876	0.94:1
TableManyItemsPerf.default	1960	2088	0.94:1
CustomToolbarPrototype.default	3606	3826	0.94:1
TreeWith60ListItems.default	214	227	0.94:1
ToolbarMinimalPerf.default	903	985	0.92:1
AlertMinimalPerf.default	247	271	0.91:1
PortalMinimalPerf.default	108	119	0.91:1
CheckboxMinimalPerf.default	2509	2795	0.9:1
Button.Fluent	492	566	0.87:1

[size-auditor]

Asset size changes

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

Baseline commit: aadad7583737319ded57925dcd6b0618e9cc4193 (build)