Ignore private members and methods from Custom Elements Manifest

Describe the bug The new setCustomElementsManifest method correctly loads a Custom Element Manifest and it populates properties in the API table, but it does not filter private members using the privacy field in the manifest.

To Reproduce https://github.com/edoardocavazza/custom-elements-manifest-private-members

Run the storybook and open docs page.

System

Environment Info:

  System:
    OS: macOS 11.3
    CPU: (12) x64 Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
  Binaries:
    Node: 15.14.0 - ~/.nvm/versions/node/v15.14.0/bin/node
    Yarn: 2.4.2 - /usr/local/bin/yarn
    npm: 7.7.6 - ~/.nvm/versions/node/v15.14.0/bin/npm
  Browsers:
    Edge: 91.0.864.48
    Firefox: 89.0
    Safari: 14.1
  npmPackages:
    @storybook/addon-actions: ^6.4.0-alpha.9 => 6.4.0-alpha.9 
    @storybook/addon-docs: ^6.4.0-alpha.9 => 6.4.0-alpha.9 
    @storybook/addon-essentials: ^6.4.0-alpha.9 => 6.4.0-alpha.9 
    @storybook/addon-links: ^6.4.0-alpha.9 => 6.4.0-alpha.9 
    @storybook/web-components: ^6.4.0-alpha.9 => 6.4.0-alpha.9

[WillGeller]

@thepassle My team would greatly appreciate a privateFields: false option on setCustomElementsManifest, we hold a similar viewpoint to @dschwank and feel that it is valuable for the CEM to have all the metadata reflective of the web components internals, but it would be great to have Storybook give us the option to hide @state() private type of properties from the Storybook docs, which is largely used to tell component library consumers the input/output API of the components, not it’s underlying implimentation.

[dschwank]

Thanks for sharing @thepassle & @WillGeller !

So let’s try to go with a privateFields option. Has anyone started with the implementation already? If not, then I would make a first draft where we could continue the discussion. ✌️