Fix #3826, sort all file lists in moz.build

[ianb]

This seems to be a new ./mach build requirement

[jaredhirsch]

Tell me more, I'm confused

[ianb]

@6a68: This is to fix an error I was getting consistently running mach build, per #3826: UnsortedError: An attempt was made to add an unsorted sequence to a list. The incoming list is unsorted starting at element 0. We expected "webextension/assertIsBlankDocument.js" but got "webextension/domainFromUrl.js"

[jaredhirsch]

Huh. My exported branch has things properly alphabetized, which explains why I wasn't able to repro the error. I can repro if I undo the ordering.

[ianb]

Probably an upstream change to fix, and your export didn't have to override the moz.build files