[core] Allow prefetching tiles for all source types

[brunoabinader]

Follow up to #7741, we should revisit this feature proposed by @tmpsantos now that #7026 is fixed.

[ChrisLoer]

Awesome, I need to remember to try this out next time I'm stuck with a slow internet connection...

[kkaefer]

@ChrisLoer To simulate slow internet connections, you can also use the "Network Link Conditioner". You can obtain it from the Additional Tools package from the Apple Developer website:

[brunoabinader]

My assumption about the failing CI tests is that we are checking if the map is loaded based on prefetched tile data. We probably need additional logic to ignore - or even disable prefetch - in still mode.

[brunoabinader]

My assumption about the failing CI tests is that we are checking if the map is loaded based on prefetched tile data. We probably need additional logic to ignore - or even disable prefetch - in still mode.

I've updated this PR to reflect the proposed idea above - we skip prefetching in static mode for two reasons: we don't need intermediary overscaled tiles when generating static images, and prefetched tiles add an extra complexity to the logic we implement for finishing a static render cycle.