[RadioGroup] Remove cloneElement, use the context

[oliviertassinari]

I have used https://github.com/palmerhq/radio-group/blob/master/src/index.tsx as inspiration.
A new feature + a smaller bundle? Deal 💸!

Closes #2225

[mui-pr-bot]

@material-ui/lab: parsed: -0.27% 😍, gzip: -0.26% 😍

Details of bundle changes.

Comparing: be889d9...28b72cc

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	-0.08%	-0.05%	351,379	351,095	90,105	90,060
@material-ui/core/Paper	0.00%	+0.02% 🔺	67,869	67,870	19,829	19,832
@material-ui/core/Paper.esm	0.00%	0.00%	60,201	60,201	18,572	18,572
@material-ui/core/Popper	0.00%	0.00%	30,460	30,460	10,529	10,529
@material-ui/core/styles/createMuiTheme	0.00%	+0.03% 🔺	17,384	17,384	5,727	5,729
@material-ui/core/useMediaQuery	0.00%	-0.19%	2,469	2,469	1,043	1,041
@material-ui/lab	-0.27%	-0.26%	148,678	148,271	43,699	43,587
@material-ui/styles	0.00%	0.00%	53,102	53,102	15,444	15,444
@material-ui/system	0.00%	-0.09%	17,136	17,136	4,529	4,525
Button	-0.46%	-0.44%	88,356	87,948	26,178	26,062
Modal	-0.49%	-0.44%	82,461	82,054	24,671	24,562
colorManipulator	0.00%	0.00%	3,232	3,232	1,299	1,299
docs.landing	0.00%	0.00%	49,958	49,958	10,837	10,837
docs.main	-0.01%	-0.01%	646,391	646,329	200,820	200,796
packages/material-ui/build/umd/material-ui.production.min.js	-0.11%	-0.13%	299,628	299,309	82,941	82,833

Generated by 🚫 dangerJS against 28b72cc