Process explorer: remove node.js/electron dependencies

[bpasero]

The process explorer depends on:

• Electron clipboard
• os node.js module (totalMem)

This should be cleaned up to be ready for sandbox by leveraging the IElectronService instead. You can take a look at the issue reporter for how to get a hold of the electron service:

vscode/src/vs/code/electron-browser/issue/issueReporterMain.ts

Line 322 in c7fe3b4

this.electronService = new ElectronService(configuration.windowId, mainProcessService) as IElectronService;

I think it would be reasonable to add another method to the electron service for accessing os.totalMem().