Expose the type parser internal API to config.ld

[Elv13]

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(this issue split of a discussion in a ticket regarding removing the sandbox and supporting modules)

Ldoc already supports creating your own types/tags using new_type, but they are mostly treated as strings. The internal version supports parsing @foo[opt=true....] arg arg2 arg3 .... It also support checking the parent (like @tparam table args \n @tparam boolean args.is_true. Currently, you have to re-implement this in your config.ld and it's impossible to fully reproduce that behavior because not enough information is exposed.