Include specific versions of jlab packages in the yarn resolution key of package.json

[jasongrout]

Especially with prerelease js packages, npm (and hence yarn) can end up with multiple versions of a package since the npm ^x.y.z does not include any packages on the next tag. We're seeing this in ipywidgets, where the base ipywidgets package can work with a number of jlab versions (including the prerelease version, but the yarn resolution algorithm doesn't count that prerelease when you have such a large range of acceptable versions), however in a prerelease we want to certainly pin the version to the prerelease js version.

So it may be useful to pin the versions of the js packages using the yarn resolution key in the staging (and dev-mode) package.json to be the exact version we want.

As a simplified example, the base widget package has a dependency on services 1||2||3||4.alpha.0, but that means the yarn resolution algorithm picks version 3 instead of version 4.alpha.0, since 3 is the latest tagged release.

[blink1073]

We did this in #6938