[heft] Create prerelease for multi-phase Heft

[D4N14L]

Summary

Merge all Heft related changes required to implement multi-phase Heft for the creation of a prerelease version. Implements much of the specification created at #3181.

Highlights:

• Converts Heft to execute using a similar pipeline to Rush instead of following a hardcoded set of tasks
• Updates heft.json to allow specification of phases and tasks
  • Each phase is made up of tasks
  • Tasks take dependencies on other tasks within the same phase
  • Phases take dependencies on other phases
• Allows for running a scoped set of actions using Rush-like syntax (ex. heft run --to build will run all phases up to and including the build phase, heft run --only build will run only the build phase)
• Heft actions are implicitly defined through phases (ex. heft build is equivalent to heft run --to build)
• Parameters are defined via JSON
  • Duplicate parameters provided by multiple plugins are allowed through the use of scoped plugins (ex. --PluginA:my-parameter and --PluginB:my-parameter parameters are created when both PluginA and PluginB define --my-parameter)
• First-class incremental watch-mode support