Add a check in the task runner to wait for dependents to finish

[i-like-robots]

What

This PR adds logic to improve the usage of the --concurrency option with a new --preserve-order flag.

Why

Running concurrent tasks is great, but not always. This is because tasks can be kicked off for packages which may depend on another package that has not yet finished running... e.g.:

• There are two modules: A and B
• A depends on B
• Both modules have a build step
• Running a build task with a concurrency of 2 would immediately kick off both builds
• The task will fail because A cannot find B

How

This PR adds an additional queue to the semaphore concurrency pattern which ensures tasks can wait until any dependent packages finish running. There are a number of changes to aid this:

1. I have refactored each action to return the package info along with the function to run the task. This was done in order to access the package name and dependencies.
2. I have added an evented queue to the "run-parallel.js" module. This will maintain a list of packages with currently queued and still running tasks. The evented queue can be asked for a promise which resolves when the queue no longer contains any dependent packages.
3. I have added an allDependencies property to the package wrapper class as this was duplicated in several places
4. I have refactored the tests to use a shared helper in order to create mock package wrappers

I tested by running various tasks within the the x-dash repository.

Show

Usage:

# long
athloi run build --concurrency 5 --preserve-order

#short
athloi run build -C 5 -P

[apaleslimghost]

really nice!

[apaleslimghost]

oops that was meant to be ✅

[magsallen]

Should there be an upper-limit to the number of tasks we can run concurrently? 🤔