feat: Minor updates to extensions template

[nickrandolph]

PR Type

What kind of change does this PR introduce?

• Feature

What is the current behavior?

Current template uses a single Extensions.props for nuget package references - this doesn't work well with VS trying to update references

What is the new behavior?

Nuget package references are in Directory.build.targets so should work better with VS for updating

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Docs have been added/updated which fit documentation template. (for bug fixes / features)
• Unit Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• Wasm UI Tests are not showing unexpected any differences. Validate PR Screenshots Compare Test Run results.
• Contains NO breaking changes
• Updated the Release Notes
• Associated with an issue (GitHub or internal)

Other information

Internal Issue (If applicable):