Accessibility fix for Dropdown, v7

[smhigley]

Cherry pick of #17603 for v7

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 74cb4cd:

Sandbox	Source
Fluent UI Button	Configuration
codesandbox-react-template	Configuration

[size-auditor]

Asset size changes

Project	Bundle	Baseline Size	New Size	Difference
office-ui-fabric-react	office-ui-fabric-react-Dropdown	227.822 kB	227.473 kB	-349 bytes

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

Baseline commit: cac66f68697f3daa33fbbb4e3a5fa262b4a35e12 (build)

[fabricteam]

Perf Analysis

No significant results to display.

All results

Scenario	Render type	7.0 Ticks	PR Ticks	Iterations	Status
BaseButton	mount	963	955	5000
Breadcrumb	mount	40685	40473	5000
Checkbox	mount	1608	1604	5000
CheckboxBase	mount	1425	1325	5000
ChoiceGroup	mount	5157	5094	5000
ComboBox	mount	1016	922	1000
CommandBar	mount	7618	7529	1000
ContextualMenu	mount	12567	12493	1000
DefaultButton	mount	1179	1178	5000
DetailsRow	mount	3697	3792	5000
DetailsRowFast	mount	3720	3712	5000
DetailsRowNoStyles	mount	3469	3545	5000
Dialog	mount	1733	1720	1000
DocumentCardTitle	mount	1802	1839	1000
Dropdown	mount	2666	2641	5000
FocusTrapZone	mount	1716	1741	5000
FocusZone	mount	1759	1788	5000
IconButton	mount	1837	1839	5000
Label	mount	320	320	5000
Layer	mount	1995	1984	5000
Link	mount	461	448	5000
MenuButton	mount	1548	1534	5000
MessageBar	mount	2073	2032	5000
Nav	mount	3328	3322	1000
OverflowSet	mount	1431	1470	5000
Panel	mount	1479	1467	1000
Persona	mount	803	824	1000
Pivot	mount	1457	1466	1000
PrimaryButton	mount	1315	1326	5000
Rating	mount	7972	7840	5000
SearchBox	mount	1314	1325	5000
Shimmer	mount	2685	2737	5000
Slider	mount	1518	1517	5000
SpinButton	mount	5126	5087	5000
Spinner	mount	402	409	5000
SplitButton	mount	3279	3312	5000
Stack	mount	492	496	5000
StackWithIntrinsicChildren	mount	1586	1588	5000
StackWithTextChildren	mount	4917	4954	5000
SwatchColorPicker	mount	10596	10495	5000
TagPicker	mount	2899	2908	5000
TeachingBubble	mount	49422	49061	5000
Text	mount	448	458	5000
TextField	mount	1416	1415	5000
Toggle	mount	837	837	5000
button	mount	110	110	5000

[msft-fluent-ui-bot]

🎉office-ui-fabric-react@v7.166.0 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Official NPM Release
• Test the release with Developer Demo Site

[msft-fluent-ui-bot]

🎉@uifabric/fabric-website-resources@v7.9.53 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Official NPM Release

[msft-fluent-ui-bot]

🎉@uifabric/fabric-website@v7.16.54 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Official NPM Release

[msft-fluent-ui-bot]

🎉@fluentui/react-examples@v0.12.21 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Official NPM Release