Remove PLATFORM_* (directives|pipes) from AngularDart

[matanlurey]

This is a formal intent to deprecate (3.X) and remove the PLATFORM_* flags from AngularDart.

i.e. the following pattern:

transformers:
    - angular2:
        platform_directives:
            - 'package:angular2/common.dart#COMMON_DIRECTIVES'
        platform_pipes:
            - 'package:angular2/common.dart#COMMON_PIPES'

Would no longer function in AngularDart 4.0.0.

Background

Originally, these flags were used to reduce code duplication across modules, as it implicitly added directives: const [ ... ] and pipes: const [ ... ] into your entire compile process. However, this greatly complicates the compile process, and actually only worked properly with barback.

In AngularDart 4.0.0+, we'll be experimenting with alternative ways to compile AngularDart, including keeping support for barback (pub transformers), but also future Dart build tools, and bazel support. Both of the latter tool sets cannot support this feature - they are modular compilers that can't resolve global application flags well.

New compiler

In 3.1+, we'll have a flag to use a brand new compiler, name pending (but internally we refer to it as the "strong compiler". It uses Dart analysis summaries - metadata produced and used by the analyzer for IntelliJ, DartDevCompiler, and more - and it means we are able to finally solve the following:

• di: Provider with useValue doesn't accept const complex data type instances #10
• Remove the need to keep implementing life cycle classes on subclasses #19
• Import additional compiler code with a prefix #153
• Component encapsulation only works with predefined constants #158
• Static class members don't work in useValue providers #218
• Support component inheritance #231
• Angular components can't cope with import aliases with providers and constructor parameters #245
• Replace OpaqueToken with Inject #288
• Support inheritance for @Input properties #291

And probably more I missed. I think we can all agree it's worth the compromise 😁

[matanlurey]

Blocked by #404.