no-bug: A few quality-of-life tweaks, take 2

[iskunk]

This should support npm run import on Windows. I looked into run-script-os, and a couple other approaches, but then figured it would be simpler to just call a small Python script that looks up the environment variable and calls cargo/$CARGO as appropriate.

Please give this a try, and let me know if you see any regressions.

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package.json: Invoke cargo(1) through a Python script that honors the CARGO environment variable if set, and pass arguments to ffprefs using the new convention (see below)

run_cargo.py: Script to invoke cargo(1), as a workaround for reading an environment variable in a package.json script in a cross-platform manner

update_service_dumps.py: Allow specifying DUMPS_FOLDER and ENGINE_DUMPS_FOLDER on the command line

ffprefs/src/main.rs: Allow specifying the prefs and engine dirs on the command line instead of hard-coding their locations relative to a common root dir

[iskunk]

I've rebased and resolved the merge conflict, and also tweaked the Linux mozconfig to allow user-set values for CC and CXX.

[mr-cheffy]

Not sure about this, maybe instead, we should just define CC and CXX if ZEN_RELEASE tests true?

[iskunk]

It's still good to set the variables generally, because the configuration might default to gcc/g++ otherwise. And the user might want to do a ZEN_RELEASE build using their compilers instead of the ones in .mozbuild/.

[mr-cheffy]

In that case, you should just use your own mozconfig file at the root directory to override these

[iskunk]

That's non-obvious, however, for just overriding the compilers. It's customary across many build systems to use CC/CXX when set in the environment, and especially when the user isn't familiar with the ins and outs of the build system, supporting common conventions like that helps make it easier to deal with.

In any event, nothing changes here unless both variables are set, to avoid any ambiguity.

[iskunk]

I've rebased and resolved the new conflicts.

Note that a big part of the reason for using Surfer in the first place is to abstract the build away from the user, so that they don't have to be familiar with the Mozilla build system in order to build Zen. Requiring the user to mess with mozconfig files, for something as basic as CC/CXX, defeats that purpose.