fix: ensure button control height matches wc root height

[chrisdholt]

Description

A bug in the website illustrated that buttons were able to get into a state where the internal control height could get out of sync with the WC height. This PR ensures the control height matches the root height.

Motivation & context

Issue type checklist

• Chore: A change that does not impact distributed packages.
• Bug fix: A change that fixes an issue, link to the issue above.
• New feature: A change that adds functionality.

Is this a breaking change?

• This change causes current functionality to break.

Adding or modifying component(s) in @microsoft/fast-components checklist

• I have added a new component
• I have modified an existing component
• I have updated the definition file
• I have updated the configuration file

Process & policy checklist

• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

[nicholasrice]

doh! I thought I fixed that!

[EisenbergEffect]

Strange, I thought I reviewed a PR just like this the other day too...