fix yellow box style in win32

[dotnetjunky]

Summary

Fix the Yellow Box style on win32.

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Description of changes

Fix the styling of YellowBox on win32. We have supported the % values for 'width' and 'height' properties, so I'm removing the forked code where we are hard coding the width of the yellow box.

However, the 'bottom' property still hasn't supported % value. Therefore, we still need to fork the code for that.

Focus areas to test

(optional)

Microsoft Reviewers: Open in CodeFlow

[PPatBoyd]

What's going wrong here that we need the width on win32 but not the other platforms?

[dotnetjunky]

On mobile, the Yellow Box covers the entire screen, and the Dismiss All button is rendered at the bottom.

On win32, somebody (probably Coates) made a change to show the maximum 3 warnings at the bottom of the UI. The Dismiss All button is rendered to the right. This is my hacky attempt to make sure the Dismiss All button is not covered by the warning texts.