chore: Make field declarations explicit

This used to be valid code:

```
class Foo {
  constructor() {
    this.bar = ‘string’;
  }
}
```

This will now fail since ‘bar’ is not explicitly
defined as a field. We now have to write:

```
class Foo {
  bar:string; // << REQUIRED
  constructor() {
    this.bar = ‘string’;
  }
}
```

modules/change_detection/test/parser/parser_spec.js

@@ -7,6 +7,9 @@ import {Formatter, LiteralPrimitive} from 'change_detection/parser/ast';
 import {ClosureMap} from 'change_detection/parser/closure_map';
 
 class TestData {
+  a;
+  b;
+  fnReturnValue;
   constructor(a, b, fnReturnValue) {
     this.a = a;
     this.b = b;