[Icon] fontSize prop not applied to Icon component

• 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 😯

The fontSize prop does not affect the <Icon /> component. Using sx doesn’t affect size either. Tested in Chrome 89.0 and Safari 14.0.

See example in the new docs. The fontSize prop doesn’t impact the size of the icons:

https://next.material-ui.com/components/icons/#font-material-icons

Expected Behavior 🤔

Expect same behavior as in v4, displayed in the current docs:

https://next.material-ui.com/components/icons/#font-material-icons

Your Environment 🌎

`npx @material-ui/envinfo`

System: OS: macOS 10.15.7 Binaries: Node: 14.15.0 - ~/.nvm/versions/node/v14.15.0/bin/node Yarn: Not Found npm: 7.6.0 - ~/Software/plynth/Current/plynth/plynth-frontend/node_modules/.bin/npm Browsers: Chrome: 89.0.4389.128 Edge: Not Found Firefox: 81.0.1 Safari: 14.0.3 npmPackages: @emotion/react: ^11.1.5 => 11.1.5 @emotion/styled: ^11.1.5 => 11.1.5 @material-ui/core: ^5.0.0-alpha.27 => 5.0.0-alpha.27 @material-ui/icons: ^5.0.0-alpha.28 => 5.0.0-alpha.28 @material-ui/lab: ^5.0.0-alpha.27 => 5.0.0-alpha.27 @material-ui/styled-engine: 5.0.0-alpha.25 @material-ui/styles: 5.0.0-alpha.27 @material-ui/system: 5.0.0-alpha.27 @material-ui/types: 5.1.7 @material-ui/unstyled: 5.0.0-alpha.27 @material-ui/utils: 5.0.0-alpha.27 @types/react: 17.0.2 react: ^17.0.2 => 17.0.2 react-dom: ^17.0.1 => 17.0.1

[mnajdova]

@luminaxster thanks for the feedback. It was a mistake at the start that we went with the same name StylesProvider. Regarding the changelog:

On release 5.0.0-alpha.24, a breaking change was listed as non-breaking:

[styled-engine] Rename StylesProvider to StyledEngineProvider ([styled-engine] Rename StylesProvider to StyledEngineProvider #24429) @mnajdova

Good catch! Seems like the PR description contain the BC description, but the changelog not.

~@siriwatknp may be a good opportunity for fixing this in https://github.com/mui-org/material-ui/pull/26948~ Nevermind, it was added in v5-alpha

[luminaxster]

This is not relevant but related: On release 5.0.0-alpha.24, a breaking change was listed as non-breaking:

• [styled-engine] Rename StylesProvider to StyledEngineProvider (#24429) @mnajdova

The failure is now observable on v5.0.0-alpha.34:

• [core] Move StyledEngineProvider to @material-ui/core/styles (#26265) @mnajdova

I confused the two providers:

import {
   ThemeProvider,
   StyledEngineProvider, // StylesProvider rename missing as breaking change in  log
   CssBaseline,
} from '@material-ui/core';
// import { StylesProvider } from '@material-ui/styles'; // I confused it with this change