Interop Gen: Support Documentation

[nikeokoronkwo]

It may be helpful for users to obtain documentation about members generated from a TS Interface. This issue addresses adding support for parsing documentation via the TS compiler for the Dart JS Interop Interface Generator.

// parses the JSDoc below
/* A cool class */
class A {

}

For now, parsing JSDoc would be done plain, unless there is need to support JSDoc Format for translation

[nikeokoronkwo]

@srujzs Would we benefit parsing certain tags from JSDoc (e.g @experimental, @deprecated, etc)