[9.20] 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 (closed)
Backport of MR !9318 (merged)