[interop] Update Configuration to allow TS Compiler Configuration and non-exported decl generation

[nikeokoronkwo]

Fixes #442
Fixes #432

This PR updates configuration and arguments to better support configuring the TS declaration generator, as well as improve support for practically using the TS declaration generator on actual libraries.

Features

• Add support for tsconfig.json: This allows configuration of the TypeScript compiler via the options available in a tsconfig.json file
• Add support for ignoring errors
• Add support for generating all declarations by default: A lot of TS declaration files may export declarations by default without specifying an export keyword, or some may handle declaration exporting differently. This allows us to generate Dart declarations for those libraries, without having to modify them and add export keywords.

[srujzs]

Let's add a small test if possible.

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Re: ignoring errors, is there a valid reason to do this? I can see it may be useful to get some output but I'm worried it might result in other failures later in our generation because we assumed the program was well-formed.

[nikeokoronkwo]

Re: ignoring errors, is there a valid reason to do this? I can see it may be useful to get some output but I'm worried it might result in other failures later in our generation because we assumed the program was well-formed.

There are few, but good, reasons to do this, mainly if we're trying to handle certain TS declarations that conflict with those built into typescript, like ES specs, DOM specs and @types/web. The code generator should work for these files, but because of errors finding symbols, the generator cannot transform declarations.

Apart from builtin TS compiler types, other use-cases shouldn't need to ignore errors.

Also: I found this a useful option as ffigen has a similar option.

[srujzs]

The code generator should work for these files, but because of errors finding symbols, the generator cannot transform declarations.

Gotcha. I suppose since it's opt-in, users know what errors they're trying to work around. It would be nice if we can allow only ignoring those missing symbols errors and leave all the other errors, but I don't know if that's possible.