[misc] Batch small changes

[oliviertassinari]

• [ClickAwayListener] Forward ref

It might be the only component that didn't forward the ref.

• [docs] Link great resources

Share the good stuff.

• [docs] Remove Rating bundle size

Eww, 20 kB.

• [docs] What's the clsx dependency for?

This is the most frequent query on Algolia with no results (0.05%).
I guess we have reached a point where we can start to ignore this metric and focus on the matching results :).

• [Slider] Add color prop

It seems that color secondary is supposed to be the default: https://material.io/components/sliders/#theming.
At least, people can easily switch.

• [core] Increase coverage of refType

Handle #17136 (comment).

• [docs] Fix Slider demo warning

Related to the new aria-label logic for a range slider.

• [Radio/Checkbox] Add customization demo

[mui-pr-bot]

@material-ui/core: parsed: +0.12% , gzip: +0.06%
@material-ui/lab: parsed: +0.28% , gzip: +0.14%

Details of bundle changes.

Comparing: ce4d844...30ed0c3

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	+0.12% 🔺	+0.06% 🔺	331,220	331,618	90,473	90,527
@material-ui/core/Paper	0.00%	0.00%	68,774	68,774	20,485	20,486
@material-ui/core/Paper.esm	0.00%	+0.01% 🔺	62,148	62,148	19,214	19,216
@material-ui/core/Popper	0.00%	-0.11%	28,466	28,466	10,188	10,177
@material-ui/core/Textarea	0.00%	0.00%	5,094	5,094	2,135	2,135
@material-ui/core/TrapFocus	0.00%	0.00%	3,834	3,834	1,617	1,617
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	16,385	16,385	5,827	5,827
@material-ui/core/useMediaQuery	0.00%	0.00%	2,541	2,541	1,058	1,058
@material-ui/lab	+0.28% 🔺	+0.14% 🔺	153,209	153,644	46,684	46,748
@material-ui/styles	0.00%	0.00%	51,494	51,494	15,304	15,304
@material-ui/system	0.00%	0.00%	15,668	15,668	4,361	4,361
Button	0.00%	-0.04%	78,663	78,663	24,048	24,038
Modal	0.00%	-0.14%	14,335	14,335	5,013	5,006
Portal	0.00%	0.00%	2,907	2,907	1,322	1,322
Rating	0.00%	+0.05% 🔺	70,016	70,016	21,864	21,875
Slider	+1.15% 🔺	+0.81% 🔺	74,282	75,137	23,015	23,202
colorManipulator	0.00%	0.00%	3,904	3,904	1,543	1,543
docs.landing	0.00%	0.00%	52,253	52,253	13,780	13,780
docs.main	+0.01% 🔺	+0.01% 🔺	597,376	597,427	190,809	190,829
packages/material-ui/build/umd/material-ui.production.min.js	+0.12% 🔺	+0.09% 🔺	302,086	302,455	86,797	86,873

Generated by 🚫 dangerJS against 30ed0c3