fix(responsive): invalid initial value being returned

[Xiaoy312]

GitHub Issue (If applicable): closes #998

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

ResponsiveExtension (binding) is returning the initial default value created by Activator.CreateInstance when the size is not available. This can cause a problem where the default value of said type is not a valid value, such as a the case for Grid.RowSpan.
User defined enums cannot be parsed.

What is the new behavior?

The initial default value returned will now be the first member defined within: Narrowest...Widest. The reasoning being that, if it is defined it has to be more valid than just the default(T).
User defined enums can now be parsed by ResponsiveExtension correctly.

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Tested the changes where applicable:
  • UWP
  • WinUI
  • iOS
  • Android
  • WASM
  • MacOS
• Updated the documentation as needed:
  • General Doc Update
  • Controls Doc Update
  • Extensions Doc Update
  • controls-styles.md
  • lightweight-styling.md (LightWeight Styling Resource Keys)
• Runtime Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• Contains NO breaking changes
• Associated with an issue (GitHub or internal)
• Commits must be following the Conventional Commits specification.