[gen-ts-declarations] Preserve JSDoc tags for properties

[web-padawan]

I would like to use JSDoc tags like @attributeor @attr for https://github.com/runem/web-component-analyzer
These tags need to be present in d.ts files in order to be picked up.

Currently, custom tags parsed by polymer-analyzer are not passed to Property formatter. I will submit a PR to fix that.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[web-padawan]

Closing as no longer relevant (we use a fork of modulizer with this change included).