Tidied CodeWriter and tweaked API for annotations/methods

[paulbalaji]

Description

Before:

• annotation defined within the lambda for methods/types/enums
• can only populate a method using Action<MethodBlock>

Now:

• do .Annotate on the parent and then call .Method/.Type/.Enum
  • e.g. ns.Annotate("Serializable").Type("public struct Foobar", t => {});
• .Method has a separate constructor taking Func<IEnumerable> instead of Action
  • e.g.

   t.Method("public static void Test()", () => new[]
   {
   	"var x = 42;",
   	"var y = 360;",
   	"return x + y;"
   });

   t.Method("public static void Test()", () => someList.some(a => wesome).linq());

Also enforced that you can only define namespace/using directives at the top-level CodeWriter

Tests

• will use for build system codegen port

Documentation

• changelog

Primary reviewers

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