Repository: flutter
Issue: Instances of the Typography class don't supply a font size.
Labels: framework,f: material design,c: proposal,P3,team-design,triaged-design

### Is there an existing issue for this?

- [X] I have searched the [existing issues](https://github.com/flutter/flutter/issues)
- [X] I have read the [guide to filing a bug](https://flutter.dev/docs/resources/bug-reports)

### Steps to reproduce

Generate an instance of Typography

`final typography = Typography.material2021();`

Access a member text style of the instance.

`final style = typography.black.displayLarge;`

Access its fontSize

`print(style.fontSize); // Null`

### Expected results

Text Styles are assigned their correct Material font size when created by an instance of the Typography class. 

### Actual results

Font size is null.

If there's a reason why `Typography` should _not_ set this, then I'd like some kind of utility class to access these sizes, as it would be very useful for creating consistent theming for my app :)

### Code sample

<details><summary>Code sample</summary>

```dart
class MyCustomTheme {
  static ThemeData getTheme() {
    int seedColor = 0xFF5D6CBD;

    ColorScheme cs = ColorScheme.fromSeed(
      seedColor: Color(seedColor),
      primary: Color(seedColor),
    );

    NavigationBarThemeData navigationBarThemeData = NavigationBarThemeData(
      backgroundColor: cs.primary,
      iconTheme: MaterialStateProperty.resolveWith((states) {
        if (states.any((s) => s == MaterialState.selected)) {
          return IconThemeData(color: cs.onPrimaryContainer);
        }
        return IconThemeData(color: cs.surface);
      }),
      labelTextStyle: MaterialStateProperty.all(
        TextStyle(color: cs.onPrimary),
      ),
    );

    AppBarTheme appBarTheme = AppBarTheme(
      backgroundColor: cs.primary,
      titleTextStyle:
          TextStyle(fontSize: 22), 
          // I'd prefer to just use Typography().black.titleLarge but 
          // fontSize isn't supplied until after the theme is created.
    );

    return ThemeData(
      useMaterial3: true,
      colorScheme: cs,
      navigationBarTheme: navigationBarThemeData,
      appBarTheme: appBarTheme,
    );
  }
}

```

</details>


### Screenshots or Video

<details>
<summary>Screenshots / Video demonstration</summary>

[Upload media here]

</details>


### Logs

-- NA

### Flutter Doctor output

<details><summary>Doctor output</summary>

```console
Flutter 3.10.6 • channel stable • https://github.com/flutter/flutter.git
Framework • revision f468f3366c (4 weeks ago) • 2023-07-12 15:19:05 -0700
Engine • revision cdbeda788a
Tools • Dart 3.0.6 • DevTools 2.23.1
    ~/dev/r/serealv2design    main !1  flutter doctor -v                                          ✔ 
[✓] Flutter (Channel stable, 3.10.6, on Manjaro Linux 6.1.41-1-MANJARO, locale en_GB.UTF-8)
    • Flutter version 3.10.6 on channel stable at /home/tduff/dev/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision f468f3366c (4 weeks ago), 2023-07-12 15:19:05 -0700
    • Engine revision cdbeda788a
    • Dart version 3.0.6
    • DevTools version 2.23.1

[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at /home/tduff/Android/Sdk
    • Platform android-34, build-tools 34.0.0
    • Java binary at: /opt/android-studio/jbr/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.6+0-17.0.6b829.9-10027231)
    • All Android licenses accepted.

[✗] Chrome - develop for the web (Cannot find Chrome executable at google-chrome)
    ! Cannot find Chrome. Try setting CHROME_EXECUTABLE to a Chrome executable.

[✓] Linux toolchain - develop for Linux desktop
    • clang version 15.0.7
    • cmake version 3.27.0
    • ninja version 1.11.1
    • pkg-config version 1.8.1

[✓] Android Studio (version 2022.3)
    • Android Studio at /opt/android-studio
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.6+0-17.0.6b829.9-10027231)

[✓] Connected device (2 available)
    • sdk gphone64 x86 64 (mobile) • emulator-5554 • android-x64 • Android 14 (API 34) (emulator)
    • Linux (desktop)              • linux         • linux-x64   • Manjaro Linux 6.1.41-1-MANJARO

[✓] Network resources
    • All expected network resources are available.

```

</details>