This PR implements

• Go-to-def onoverride keyword selects the overridden method declaration.
• Go-to-def on a modifier or keyword that starts a declaration works the same as go-to-def on the declaration name.
• Go-to-def on label inbreak orcontinue statement selects the label definition.
• Go-to-def oncase ordefault keyword selects the containingswitch statement.
• Go-to-def onreturn,yield orawait keyword selects the containing function declaration.
• Go-to-def on a call expression selects the the signature chosen by overload resolution.
• Go-to-def on a property in an object literal with a contextual type selects the declaration in the contextual type.
• Go-to-def on a property with no explicit declaration selects the index signature(s) for the property.
• Go-to-type-definition on a variable or property selects the associated type(s).
• Go-to-type-definition on a variable with a generic type such asT[] selects both declarations ofT andArray.

The PR also movesgetErrorRangeForArrowFunction andGetErrorRangeForNode frombinder.go toscanner.go (where other similar functions reside).