Add a one sentence summary for ol.geom.* exportable symbols

[marcjansen]

This PR adds basic documentation to @api symbols of ol.geom*. This never ends...

Please review.

See also

• Add docs for exportable symbols #3488: first batch of docs by @tschaub
• Add a one sentence summary for all exportable symbols. #3497: overview issue of missing docs
• Add a one sentence summary for ol.proj.* and ol.layer.* exportable symbols #3583: docs for ol.proj.*, ol.layer.*
• Add a one sentence summary for ol.source.* exportable symbols #3580: docs for ol.source.*
• Add a one sentence summary for ol.interaction* exportable symbols #3613: docs for ol.interaction*

[tschaub]

This is something we'll probably have to deal with, but the builder client doesn't do any special parsing of JSDoc's custom @lnk style annotations. It would reduce work in the near-term to just have plain text for the first sentence (subtle, but the description for #3497 does specify plain text).

[tschaub]

Nice @marcjansen. Since my comment above applies to a number of commits and also reflects an issue with current docs, I don't think you have to deal with it here. We can regex our way around the @link annotations in the build client.

[marcjansen]

Cool, thanks, @tschaub.