Add an option to disable parallel building of targets

[softworkz]

Use case

Using hooks like artifactBuildStarted and artifactBuildCompleted to manipulate any content in outDir doesn't work out well when building targets which are executed in parallel.

Since electron-builder makes a number of unfortunate hardcoded decisions, using hooks like above is sometimes the last rescue - but it only works when the changes you make are only going into the intended target. To ensure that, an option is needed to disable the parallel execution.

Temporary Workaround

exports.default = async (ctx) => {

    for (let i = 0; i < ctx.targets.length; i++) {
        ctx.targets[i].isAsyncSupported = false;
    }
};

Thanks

[softworkz]

Related: Is it possible to run afterPack on a per-target basis?