fix(dart/transform) Merge setter registrations with the same name

[kegluneq]

Currently we generate one setter registration per bind value. For example, this annotation:

'bind': {'text': 'tool-tip'}

attached to two classes, A and B would generate

registerSetters({'text': (A obj, String value) => obj.text = value})
registerSetters({'text': (B obj, String value) => obj.text = value})

Instead we need to generate a single setter registration using a common parent class of A and B. This would be tough to do without resolving in our transformer, which we would like to avoid. As a first approximation, we can omit the parameter type (A and B above) which will be interpreted as dynamic.

To do this, we need global knowledge of the setters which would be registered.

1. Modify the bind_generator transformer, its primary inputs are the .ngDeps.dart files generated by the app entry points.
2. Parse these files, gathering information on the setters to be generated.
3. Also parse all .ngDeps.dart files imported by the primary inputs.
4. Where there are multiple setters for a single property, remove type information from the registered setter.
5. Output a .ngSetters.dart file with a setupReflection method that registers all setters.
6. Generate code to import and call setupReflection during app setup.

[kegluneq]

After spending some more time thinking about this, the method above will not work because it will no longer be safe to use imports from the .dart file in a .ng_deps.dart file if we need to generate all setters into a single file.

I haven't spent much time thinking about this, but since the reflector passed into setupReflection is untyped, perhaps it would be easiest to generate a ReflectorWrapper that gathers the setters from all .ng_deps.dart files and registers the appropriate setter.

[mhevery]

@kegluneq Can this be closed?