Data inspection support for ES6 Sets, Maps, and Generators

[weinand]

test item for microsoft/vscode-node-debug#51 and microsoft/vscode-node-debug#41:

• Windows - @bpasero
• OS X - @seanmcbreen
• Linux - @aeschli

VS Code node debugging no longer shows ES6 Sets, Maps, and Generators as undefined or empty objects.

Map:

Set:

Generator:

Verify that:

• Maps and Sets show their contents in an array like way. Each slot has a sequence number because Maps and Sets preserve insertion order.
• Large Maps and Sets are fast and show their contents in chunks
• Generators show the state of the generator (e.g. 'suspended' or 'closed').