Move executeCommandLine.ts into its own project

[weswigham]

It being in two projects (tsc and testRunner) simultaneously is probably already causing interesting things with our current build, and when transformed, it ends up getting emitted multiple times (each time from a different program, checked in a different way, against different interfaces). This causes some stuff to go poorly (namely namespace references get mangled).

So this fixes that by moving it into its own project, on which both tsc and testRunner depend (it, in turn, depends on compiler, like tsc). This is much more in-line with how project references are supposed to be used for a situation like this.

[sandersn]

Seems fine, although I've spent little time thinking about our project structure.

[weswigham]

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