feat(spdx_license): include tryParse

[alestiago]

Description

Adds a tryParse method to validate future CLI user inputs when white/black listing certain licenses. unknown will be a valid license type but erroneous input (for example, MIP instead of MIT) should throw an exception for a better user experience.

Changes:

• Modified parse to throw a FormatException when failed to parse (similar to int.parse)
• Included tryParse to return null if can't be parsed (similar to int.tryParse)

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore