Clean up query_stats_errored.js after all reads tests are added.

Some things to clean up:

• Reorganize as one outer describe per topology (standalone / replset / sharded), with non-cursor vs. cursor errors as nested describes. Right now, there are 2 standalone blocks that start 2 mongods to run the same coll.drop + insert on 3 docs
• assertOnlyErroredEntry() and assertErroredCursorEntry() share most of the same logic - could be cleaned up + moved to query_stats_utils.js
• Add an assertNoErrorsRecorded(metrics) helper function to check execCount, execCountErrored, !hasOwnProperty("errors")
• getMore() and changeStreamGetMore() are identical + can be collapsed into a helper
• The execErrorCases table (find/aggregate/count/distinct) is written twice, once for mongod and once for mongos. It can be moved out and defined once
• Move withFailPoint() above all describes and use it everywhere. Right now, the mongod blocks hand-roll configureFailPoint / try / finally fp.off() multiple times