`Renderer::clearData()` is a better API than the removed `MapOptions::keepRenderData()`:
- gives more flexibility to the client
- similar to the existing `Renderer::reduceMemoryUse()`
- the `MapOptions::keepRenderData()` API implementation could not handle the raise condition, which
happened if the new still image request had come before all tiles from the previous requests were loaded.
Co-authored-by: Dane Springmeyer <dane@mapbox.com>