Run terminal command after emit with tsc CLI

[alshdavid]

In order to apply a post-processing step to typescript files, such as path resolution or migrating files from source directories, it would be useful to have access to a post-emit hook.

tsc -w --post-emit="ls dist"

This would run ls dist every time the compiler emits on watch mode.

[RyanCavanaugh]

This is outside the scope of things we want TS to be responsible for