Add a function for efficiently indexing a set of input points to a raster block or chunk index

For multi-block raster chunks defined on natural block boundaries, or single-block chunks. Given inputs: * x, y point locations * a raster block or chunk index matrix as returned by `GDALRaster::get_block_indexing()` / `GDALRaster::make_chunk_index()` efficiently index the points to the block/chunk they are contained by, e.g., `index_pts_to_chunks()`.