chg: test: Reduce the size of hashmap_nodes.h file

Instead of keeping the whole array of test_node_t objects, just keep the
hashvalues and generated the rest of the test_node_t on the fly.  The
test still works this way and the file size has been reduced from 2M to
90k.

Closes #4851

Merge branch '4851-generate-problematic-isc_hashmap-test-data' into 'main'

Closes #4851

See merge request isc-projects/bind9!9318