Adds Heft tasks. Closes #618

[Adam-it]

🏗️ Work in progress

This is still work in progress and we may not merge it just yet as this was developed based on SPFx 1.22-beta.4 so still some things may change before the official GA, but this PR should give us a head start when it comes to adding heft tasks support to this extension

🎯 Aim

The aim is to refactor the task view to show heft tasks in case the SPFx project uses primary heft for build toolchain tasks

📷 Result

SPFx 1.22 with Heft

SPFx 1.21 with Gulp

✅ What was done

• Refactored the icons and naming a bit
• Added heft tasks to the task view in case the project uses heft npm package
• Update Task View tests to support heft
• Optimize code, currently most is duplicated but it seems many methods may be reused and we only need to pass if gulp or heft should be used in the command
• It seems heft does not support start (previously serve) with a specific configuration, like for command sets. Left a TODO for it in code and checking this with SPFx team

🔗 Related issue

Closes: #618