[UWP][TextBox] Entering 14K+ characters causes sample to break

[StewartPolsky]

Current behavior

Expected behavior

User should be able to view and modify TextBox contents

How to reproduce it (as minimally and precisely as possible)

1. Launch app
2. Navigate to any sample that has a TextBox (ex. Binding)
3. Enter around 14000 Characters
4. Notice that a large grey square is displayed

NOTE Issue can be reproduced in any sample with a TextBox, both Material and Fluent

Environment

Nuget Package:

Package Version(s):

Affected platform(s):

• [ ] iOS
• [ ] Android
• [ ] WebAssembly
• [ ] WebAssembly renders for Xamarin.Forms
• [x] Windows
• [ ] Build tasks

Visual Studio:

• [ ] 2017 (version: )
• [x] 2019 (version: )
• [ ] for Mac (version: )

Relevant plugins:

• [ ] Resharper (version: )

Anything else we need to know?