Clear and concise description of the problem

The typespec should add validation to @pattern or Azure specific linting rule for RegEx.

Recently we encountered an invalid regex expression.

The correct expression should be @pattern("^[^_\\W][\\w\\-._]{0,79}(?<![-.])$")

Checklist

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.