Avoid append only cache in WebGL tile layers

[tschaub]

The WebGL tile renderer maintains its own cache of tile textures. When a layer is configured with an explicit cacheSize, this is passed to the renderer's cache. And the intention is that the source's cache remains near empty. In #12671, the cache size for the data tile source was set to 0.1 to make sure it stays empty. But for all other tile sources, the source's tile cache has a size of 0 or unlimited.

The Canvas tile renderer calls source.updateCacheSize() to manage the cache on its layers' sources. This change makes the WebGL tile renderer do the same. (Having the renderer reach through the layer and the source to manage the tile cache is further support for moving the cache to the renderer instead of the source.)

Fixes #13927.

[github-actions]

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[ahocevar]

Thanks!

[ahocevar]

(Having the renderer reach through the layer and the source to manage the tile cache is further support for moving the cache to the renderer instead of the source.)

If we do that, we might consider doing it in a way that the same source can still be used in more than one layer, without having to have its own cache for each layer renderer.