Adaptor docs sometimes pulls down too much data (and so is slow)

This issue doesn't technically belong here, it's kind of a cross-repo thing. But it's impact is here and it can be managed more effectively from here I think.

The Issue

When loading documentation for some pre-monorepo adaptors, the client can download far more information than it needs. language-common@1.7.1 for example, downloads hundreds of files (!!), meaning it takes docs a lot longer to generate than it should.

The problem is:

• adaptor-docs asks kit/describe-package for metadata about a package
• describe-package loads the package.json manifest for that package, and downloads every d.ts file listed in the files array
• Some (all?) adaptor package.jsons list files from its node_modules - files which surely shouldn't be listed.

It is probably worth examining the impact a bit more before deciding the severity of this. To be fair I think it's quite a simple fix.

Solutions

Probably the best fix is in kit/describe-package. When fetching a file listing from npm, we simply ignore anything that starts with node_modules.

An alternative is to wait for the doc builder to move out of the client and into the server (see #492). With caching in place the impact of this is greatly reduced. We may consider fixing describe-package but it'll be less critical.

Start with adaptor-docs and kit/describe-package, then inspect how the package.json files array is used when fetching the language-common@1.7.1 file listing. Confirm the excess downloads and determine whether node_modules entries can be ignored there; done means documentation generation no longer fetches those unnecessary files.