[SelectInput] Convert to function component

[joshwooding]

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

Works towards #15231

[mui-pr-bot]

@material-ui/core: parsed: -0.26% 😍, gzip: -0.17% 😍

Details of bundle changes.

Comparing: 3044cb4...b175c50

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	-0.26%	-0.17%	312,618	311,790	84,447	84,305
@material-ui/core/Paper	0.00%	-0.02%	67,279	67,279	19,968	19,965
@material-ui/core/Paper.esm	0.00%	0.00%	60,640	60,640	18,884	18,884
@material-ui/core/Popper	0.00%	-0.03%	34,907	34,907	11,812	11,809
@material-ui/core/Textarea	0.00%	0.00%	5,327	5,327	2,291	2,291
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	15,898	15,898	5,771	5,771
@material-ui/core/useMediaQuery	0.00%	0.00%	2,106	2,106	974	974
@material-ui/lab	0.00%	-0.00%	141,612	141,612	42,722	42,721
@material-ui/styles	0.00%	0.00%	50,833	50,833	15,013	15,013
@material-ui/system	0.00%	0.00%	11,765	11,765	3,928	3,928
Button	0.00%	-0.02%	85,621	85,621	25,588	25,584
Modal	0.00%	-0.00%	79,901	79,901	24,011	24,010
colorManipulator	0.00%	0.00%	3,904	3,904	1,543	1,543
docs.landing	0.00%	0.00%	50,908	50,908	11,210	11,210
docs.main	0.00%	0.00%	648,518	648,518	201,926	201,926
packages/material-ui/build/umd/material-ui.production.min.js	-0.28%	-0.26%	293,911	293,076	82,492	82,277

Generated by 🚫 dangerJS against b175c50

[oliviertassinari]

Awesome work! I have tried something new with this review: 1. Checkout the pull request. 2. Revert the source back to its original state. 3. Make sure the new tests are green.

[joshwooding]

Awesome work! I have tried something new with this review: 1. Checkout the pull request. 2. Revert the source back to its original state. 3. Make sure the new tests are green.

I try to do this when re-writing the tests :)

[eps1lon]

Awesome work! I have tried something new with this review: 1. Checkout the pull request. 2. Revert the source back to its original state. 3. Make sure the new tests are green.

This is something I'll try to do with all my PRs: Tests before implementation. This way it's easier for reviewers to verify: is it a bug? would this test new behavior properly etc. Then you can share different implementations based on the same test plan via git branches. If you do impl after test this becomes very weird (hard reset, rebase etc).