Add support for webview.hide() and webview.collapse() in the API

[SolidCAMLATAM]

I'd like to be able to programatically collapse or hide a webview.

This is helpfull with extensions that use multiple webviews, for user inputs, settings configuration, integration with other tools. The UI can easily become polluted.

For reference, currently we have the method show(), but there's no hide().

Other vscode API areas, like the exhibition of trees, have more symmetry like reveal() and collapse().