Fix deprecation warnings from MUI > 4.12.X

[MoritzHorch]

In Material-UI 4.12.X several styling deprecations errors were introduced. Especially the fade color utility which is used many times in this project. Now I know that active development has been moved to Material-UI V5, but I think we should at least have fixes for such console-spamming errors as long as Material-UI V5 is still not a stable release and especially when the new pickers are only a part of the lab.

• The issue is present in the latest release.
• I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

When using and opening DatePicker in combination with the MuiPickersUtilsProvider the following error will be logged to the console:

Material-UI: The fadecolor utility was renamed toalpha` to better describe its functionality.

You should use import { alpha } from '@material-ui/core/styles' at ... at MuiPickersUtilsProvider at ...

Or: Warning: Failed prop type: The prop justifyofForwardRef(Grid)is deprecated. UsejustifyContent instead, the prop was renamed.

Expected Behavior 🤔

No deprecation error should be logged and the suggested utilitly / property should be used.

Steps to Reproduce 🕹

Steps:

1. Open https://codesandbox.io/s/eager-drake-6wqck
2. Open the pickers one by one
3. See several deprecation logs arise

Context 🔦

This issue heavily disturbs working with the current stable release and right now we do not feel like that using the beta- and lab channels is the right way to go in production apps.

Your Environment 🌎

"@material-ui/core": "4.12.1",
"@material-ui/pickers": "3.3.10",
"moment": "2.29.1",
"@date-io/moment": "1.x",
"react": "latest",
"react-dom": "latest",
"react-scripts": "latest"

[MonstraG]

Same thing here, updated to MUI v4.12.X to simplify migration when v5 finally comes out, hit this.

[oliviertassinari]

We have archived this repository, more details in #2157.