Fix describing type with table in schema

[DifferentialOrange]

Rework of #22

Before this PR, describing argument type in schema with a table resulted in "No value provided" error on query execution and in "unsupported Lua type 'function'" error on variable type validation.

Reworks: introduce tests, separate from descriptions commit.

[Totktonada]

Looks hacky, but I can't propose a better solution. At least, tests are passed. Feel free to proceed.

I suggest to leave comments here with brief explanation, why such tweaks are legal and don't break anything. And why they're needed.

[DifferentialOrange]

Looks hacky, but I can't propose a better solution. At least, tests are passed. Feel free to proceed.

I suggest to leave comments here with brief explanation, why such tweaks are legal and don't break anything. And why they're needed.

We already support describing output arguments type with table, for example, here:

graphql/graphql/execute.lua

Line 310 in e9590db

if argument.kind then argument = argument.kind end

It doesn't break existing behavior, it just adds additional support which is consistent to existing one. Why do we need it? For correct support of input arguments descriptions.

[Totktonada]

So it is purely to support this new way to delare arguments in the schema? Well, how about commenting all blocks, which are for supporting it? I'm pretty sure that it is not obvious from the code itself.

[DifferentialOrange]

So it is purely to support this new way to delare arguments in the schema? Well, how about commenting all blocks, which are for supporting it? I'm pretty sure that it is not obvious from the code itself.

Added comments near lines of code.