Add interpolation and caching in DefaultEvaluator

The default, implementation of GridCoverage.evaluator() returns an instance of the package-private DefaultEvaluator class. The apply(DirectPosition) method of that class requested a RenderedImage of size 1×1 pixel every times that the method is invoked. This is inefficient. We should request an image of the size of a tile, for example 512×512 pixels, and cache it.

This work may require the completion of TileMatrix work, because we may try to align the requests to the size and position of existing tiles.

Having larger sizes also allow the use of bilinear or other interpolations, which are currently not implemented in DefaultEvaluator.