Vendor Go 1.14 filepath.EvalSymlinks code
As discussed #439 (closed) we want to integrate the "virtual filesystem" code of the proof of concept in !315 (closed).
This MR adds the heart of the implementation of the standard library filepath.EvalSymlinks
function. I am submitting this as-is so that in later MR's it will be easier to review what is and is not changing relative to the stdlib version.
Edited by Jacob Vosmaer