Scopes: Define exact scope start/end requirements for generators (in terms of JavaScript AST)

[szuend]

This came up a couple of times but we should spell out explicitly for each JavaScript language scope where we expect generated ranges to start/end. Debuggers (Firefox DevTools, Chrome DevTools) need to be able to match generated ranges to the scopes that all out of the engine.

For example, generated ranges for a JavaScript should start at the opening paren ( and end at the closing curly }. We should spell this out for all scope types in the JavaScript language.

[szuend]

Duplicate of #76