Document types for unexported symbols

[ahocevar]

With this change, we get documentation for the type of
ol.render.Event#vectorContext, and other types of unexported
symbols.

[tschaub]

@ahocevar shouldn't we instead be exporting properties like vectorContext if we want them used (and documented)?

[ahocevar]

@tschaub You mean so we can get rid of externs/oli.js? Let me try if that works.

[tschaub]

@ahocevar sorry, not sure it is actually possible. There has been discussion before about not being able to export prototype properties, and this is the whole reason for oli.js I guess. I'd need to dig a bit to get the complete picture.

[ahocevar]

At least for ol.render.RenderEvent it works when marking context, vectorContext etc. as @todo api in the custom-build branch.

[ahocevar]

Scratch that. oli.js is needed. However, I'm working on a better approach now, by making @interface a known JSDoc tag.

[ahocevar]

d12c2ec, which is the better approach mentioned above, solves this issue on top of #1979.