Improve cache eviction strategy

[kkaefer]

Our offline database cache currently evicts tiles based on a least recently used strategy. With an API like #2006 that would allow prefetching tiles along a path or at a destination, we'd need the ability to control cache eviction to prevent those unused tiles from getting evicted from the cache.

We should think about whether we can instead calculate a score based on multiple factors to decide whether we should remove something from the cache. Potential metrics that could go into the score are:

• Last use date
• Zoom level (favor lower zooms as they cover more area)
• Distance from current position
• Distance from specified prefetching path(s)

/cc @d-prukop

[halset]

Could it be an option to have different eviction strategies? As an start, the following two:

• The current strategy.
• A no evict strategy that basically has an empty evict method. The deleteRegion method will have to delete tiles exclusively to the deleted region, not just rely on the evict method. I do this in my app and it works well for such an offline heavy app.

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.