[docs] Improve lighthouse a11y score in demos

[eps1lon]

Audited every component demo with lighthouse a11y audit using https://github.com/eps1lon/mui-scripts-incubator. The following issues were not fixed because they are caused by 3rd party libraries:

• carbon ad links have discernible text
• codefund ad links have discernible text
• codefund images have alt text
• various issues in /components/table (all caused by material-table, they upgraded to v4, will investigate new version in separate PR)
• invalid usage of aria-readonly in virtualized table demo (fixed by fix(Table): aria-readonly is not allowed on rowgroup bvaughn/react-virtualized#1380)

There's also an issue with iframes having no title. Will followup in a different PR once #15874 is resolved. Applied in this PR since it directly relates to demos

Fixes can be grouped into the following categories:

• missing aria-label
• label not being associated to inputs (fixed with aria-labelledby)
• aria-controls (was aria-owns) pointing to elements that aren't part of the DOM. They should be otherwise aria-controls doesn't add value. aria-controls is used in https://www.w3.org/TR/wai-aria-practices/examples/menu-button/menu-button-links.html
• ul not containing li or li being part of div

[mui-pr-bot]

Details of bundle changes.

Comparing: b4de19a...5a2b1ba

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	0.00%	0.00%	315,057	315,057	86,304	86,304
@material-ui/core/Paper	0.00%	0.00%	67,921	67,921	20,184	20,184
@material-ui/core/Paper.esm	0.00%	0.00%	61,217	61,217	18,981	18,981
@material-ui/core/Popper	0.00%	0.00%	28,740	28,740	10,345	10,345
@material-ui/core/Textarea	0.00%	0.00%	5,513	5,513	2,376	2,376
@material-ui/core/TrapFocus	0.00%	0.00%	3,744	3,744	1,573	1,573
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	15,978	15,978	5,787	5,787
@material-ui/core/useMediaQuery	0.00%	0.00%	2,106	2,106	975	975
@material-ui/lab	0.00%	0.00%	138,866	138,866	42,660	42,660
@material-ui/styles	0.00%	0.00%	51,386	51,386	15,193	15,193
@material-ui/system	0.00%	0.00%	14,463	14,463	4,181	4,181
Button	0.00%	0.00%	83,901	83,901	25,459	25,459
Modal	0.00%	0.00%	20,343	20,343	6,685	6,685
colorManipulator	0.00%	0.00%	3,904	3,904	1,543	1,543
docs.landing	0.00%	0.00%	55,977	55,977	14,042	14,042
docs.main	+0.04% 🔺	+0.05% 🔺	648,696	648,947	204,571	204,664
packages/material-ui/build/umd/material-ui.production.min.js	0.00%	0.00%	293,979	293,979	83,766	83,766

Generated by 🚫 dangerJS against 5a2b1ba

[mbrookes]

Nice job!

[eps1lon]

@mbrookes Could you take a look at aacc9fd ? Add labels/labelledby to every nav element on pages where it appears multiple times i.e. the layout examples don't require a label according to the WAI-ARIA source because on those pages nav only appears once (already indicating it's the primary navigation).

[mbrookes]

Could you take a look at aacc9fd

LGTM (pending the list semantic HTML PR).

[mui-pr-bot]

Details of bundle changes.

Comparing: b4de19a...6bdf61d

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	0.00%	0.00%	315,057	315,057	86,304	86,304
@material-ui/core/Paper	0.00%	0.00%	67,921	67,921	20,184	20,184
@material-ui/core/Paper.esm	0.00%	0.00%	61,217	61,217	18,981	18,981
@material-ui/core/Popper	0.00%	0.00%	28,740	28,740	10,345	10,345
@material-ui/core/Textarea	0.00%	0.00%	5,513	5,513	2,376	2,376
@material-ui/core/TrapFocus	0.00%	0.00%	3,744	3,744	1,573	1,573
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	15,978	15,978	5,787	5,787
@material-ui/core/useMediaQuery	0.00%	0.00%	2,106	2,106	975	975
@material-ui/lab	0.00%	0.00%	138,866	138,866	42,660	42,660
@material-ui/styles	0.00%	0.00%	51,386	51,386	15,193	15,193
@material-ui/system	0.00%	0.00%	14,463	14,463	4,181	4,181
Button	0.00%	0.00%	83,901	83,901	25,459	25,459
Modal	0.00%	0.00%	20,343	20,343	6,685	6,685
colorManipulator	0.00%	0.00%	3,904	3,904	1,543	1,543
docs.landing	0.00%	0.00%	55,977	55,977	14,042	14,042
docs.main	+0.04% 🔺	+0.05% 🔺	648,696	648,947	204,571	204,664
packages/material-ui/build/umd/material-ui.production.min.js	0.00%	0.00%	293,979	293,979	83,766	83,766

Generated by 🚫 dangerJS against 6bdf61d