Test support for "related resources" in loadedScripts view

[weinand]

Test for #62034:

• macOS: @roblourens
• windows: @isidorn

Complexity: 2

Authors: @weinand

The loaded scripts view now shows related resources as children and node-debug (legacy) returns source-map sources as "related resources" via DAP.

In addition the elements of the loaded scripts view now support icon themes (only exception: top level session nodes have no icons because icon themes don't provide session icons).

The resulting UI looks like this:

Setup:

• debug a project that transpiles to JS and has source maps,
• since this feature is only implemented in node-debug (legacy) use a node.js version < 8.0 (e.g. by using "runtimeVersion": "7.10.1" in the launch config.

A good example is the node-debug (legacy) itself (e.g. its "Server" launch config).

Verify:

• source is shown as children of its corresponding JS
• scripts and related resources show correct icons and hovers
• selecting related resources opens the correct source in the editor
• setting breakpoints in related resources works