Repository: flutter
Issue: SelectableText has a slight extra padding compared to Text
Labels: framework,f: material design,a: quality,a: typography,has reproducible steps,found in release: 2.6,found in release: 2.8,team-design,triaged-design

## Steps to Reproduce

(This is on Windows desktop, I don't know about other platforms). 
1. Create two `Text` widgets that are right next to each other (eg. in a `Row`). 
2. Change the left one to `SelectableText`. 
3. Note a small space between the widgets that doesn't exist when they're just `Text`. 

`Text`:
![image](https://user-images.githubusercontent.com/14959769/145741726-52eac0aa-7c5b-4bd5-b27d-79b9a139b0e2.png)

`SelectableText`:
![image](https://user-images.githubusercontent.com/14959769/145741703-a99b84ad-a9d9-46a2-9fe3-dcde98cb01e9.png)

**Expected results:**
They have the same (lack of) spacing. The extra padding makes it hard to place texts right beside each other. 

**Actual results:** <!-- what did you see? -->

<details>
<summary>Code sample</summary>

```dart
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return MyAppState();
  }
}

class MyAppState extends State<MyApp> {
  late TextEditingController controller;
  late FocusNode focusNode;

  @override
  void initState() {
    super.initState();
    controller = TextEditingController();
    focusNode = FocusNode();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(),
      home: Scaffold(
        appBar: AppBar(
          title: Text("Test"),
        ),
        body: Row(
          children: [Text("text 1"), Text("text 2")],
        ),
      ),
    );
  }
}

```

</details>

<details>
  <summary>flutter doctor -v</summary>

```
[√] Flutter (Channel stable, 2.8.0, on Microsoft Windows [Version 10.0.22000.348], locale en-CA)
    • Flutter version 2.8.0 at D:\Portable Programs\flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision cf44000065 (4 days ago), 2021-12-08 14:06:50 -0800
    • Engine revision 40a99c5951
    • Dart version 2.15.0

[!] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
    • Android SDK at D:\Android_SDK
    X cmdline-tools component is missing
      Run `path/to/sdkmanager --install "cmdline-tools;latest"`
      See https://developer.android.com/studio/command-line for more details.
    X Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/docs/get-started/install/windows#android-setup for more details.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop for Windows (Visual Studio Community 2019 16.11.5)
    • Visual Studio at C:\Program Files (x86)\Microsoft Visual Studio\2019\Community
    • Visual Studio Community 2019 version 16.11.31729.503
    • Windows 10 SDK version 10.0.19041.0

[√] Android Studio (version 4.0)
    • Android Studio at C:\Program Files\Android\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 1.8.0_242-release-1644-b01)

[√] IntelliJ IDEA Ultimate Edition (version 2021.2)
    • IntelliJ at C:\Program Files\JetBrains\IntelliJ IDEA 2021.1.3
    • Flutter plugin version 63.0.3
    • Dart plugin version 212.5632

[√] Connected device (3 available)
    • Windows (desktop) • windows • windows-x64    • Microsoft Windows [Version 10.0.22000.348]
    • Chrome (web)      • chrome  • web-javascript • Google Chrome 96.0.4664.93
    • Edge (web)        • edge    • web-javascript • Microsoft Edge 96.0.1054.29

! Doctor found issues in 1 category.
```

</details>