Debug protocol: Please add Variable::settable

[vadimcn]

• VSCode Version: 1.4
• OS Version: All

When a debug adapter reports that is supports setVariable, all leaf variables become editable, but compound objects do not. While a reasonable heuristic, this is not optimal because:

• primitive values may be not editable if they are "synthetic" i.e. generated by a visualizer.
• compound objects may be editable, e.g. std::string (which may still want to show individual characters as children, and possibly provide a "raw" view of the implementation as a synthetic child).

I'd suggest adding an explicit "settable" flag into Variable.

[weinand]

This issue was moved to Microsoft/vscode-debugadapter-node#53