Factor out code repeat in functions calling spider_check_and_init_casual_read()

The following ha_spider methods inside ha_spider.cc call spider_check_and_init_casual_read()

ft_read_internal multi_range_read_next_first
index_first_map_internal multi_range_read_next_next
index_last_internal range_read_first_internal
index_read_last_map_internal rnd_next_internal
index_read_map_internal

Near the callsite is about 80 lines of repeated code. Part of the repeated region is also a common pattern found in other spider files and functions. They need to be factored out.

See the attached gif for an IDE demo, as well as attached .cc files with these functions extracted out (at 11.0 941f91edbc3d3a0a184b9bfc58d5e4042c4b65f1).