[core] Remove all .defaultProps usages

[joshwooding]

• I have followed (at least) the PR section of the contributing guide.

Why not? Finishes a section of #15231

[mui-pr-bot]

@material-ui/core: parsed: +0.13% , gzip: +0.07%

Details of bundle changes.

Comparing: 86de525...fd024b2

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	+0.13% 🔺	+0.07% 🔺	327,440	327,857	90,326	90,388
@material-ui/core/Paper	+0.06% 🔺	+0.06% 🔺	68,438	68,478	20,394	20,407
@material-ui/core/Paper.esm	+0.06% 🔺	+0.06% 🔺	61,721	61,761	19,178	19,190
@material-ui/core/Popper	0.00%	0.00%	28,942	28,942	10,407	10,407
@material-ui/core/Textarea	0.00%	0.00%	5,505	5,505	2,365	2,365
@material-ui/core/TrapFocus	0.00%	0.00%	3,753	3,753	1,576	1,576
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	16,160	16,160	5,813	5,813
@material-ui/core/useMediaQuery	0.00%	0.00%	2,595	2,595	1,104	1,104
@material-ui/lab	+0.05% 🔺	+0.07% 🔺	138,023	138,091	42,537	42,566
@material-ui/styles	+0.08% 🔺	+0.08% 🔺	51,847	51,887	15,371	15,384
@material-ui/system	0.00%	0.00%	15,576	15,576	4,433	4,433
Button	+0.05% 🔺	+0.04% 🔺	81,121	81,161	24,768	24,779
Modal	0.00%	0.00%	14,514	14,514	5,094	5,094
Portal	0.00%	0.00%	3,471	3,471	1,573	1,573
Slider	+0.05% 🔺	+0.04% 🔺	75,123	75,163	23,304	23,313
colorManipulator	0.00%	0.00%	3,904	3,904	1,543	1,543
docs.landing	0.00%	0.00%	54,338	54,338	13,762	13,762
docs.main	+0.06% 🔺	+0.08% 🔺	647,952	648,353	204,174	204,341
packages/material-ui/build/umd/material-ui.production.min.js	+0.12% 🔺	+0.14% 🔺	299,853	300,226	85,939	86,063

Generated by 🚫 dangerJS against fd024b2

[Izhaki]

Why were .defaultProps removed?

There are quite a few issues/commits related to this, but I couldn't find in any the reason for this (react-docgen? Functional components?). Can anyone explain, or link to the explanation?

[oliviertassinari]

@Izhaki 1. Simpler 2. React talks about potential removal 3. required for getThemeProps() usage.

[joshwooding]

Why were .defaultProps removed?

There are quite a few issues/commits related to this, but I couldn't find in any the reason for this (react-docgen? Functional components?). Can anyone explain, or link to the explanation?

https://twitter.com/dan_abramov/status/1133878326358171650?lang=en

https://github.com/reactjs/rfcs/blob/createlement-rfc/text/0000-create-element-changes.md