refactor(NODE-4632): async await in MongoClient, ClientSession, and AbstractCursor

[nbbeeken]

Description

NODE-4632

What is changing?

• src/change_stream.ts and src/collection.ts and src/cursor/find_cursor.ts and src/db.ts and src/mongo_types.ts and src/operations/drop.ts
  • spelling mistakes
• src/connection_string.ts and test/unit/connection_string.test.ts and test/unit/mongo_client.test.js
  • refactor resolveSRVRecord to be async, wrap dns APIs in promisify
  • validateLoadBalancedOptions now throws since the error does not need to be passed to a callback
• src/cursor/abstract_cursor.ts
  • Implement the async iterator using native syntax when a custom promise is not set. I think this is important to do now ensuring is maintains the expected behavior so when we drop custom promise support we don't miss something in the other API removals/changes that would be part of the major.
  • Utilize the async iterator for toArray and forEach
  • promifisify next - we may want to make this really async in a follow up.
  • ditto cleanupCursor
• src/encrypter.ts
  • async connectInternalClient, this method is internal, does not need to support maybeCallback
• src/gridfs/download.ts and test/integration/gridfs/gridfs_stream.test.js
  • remove nextTick usage, the callback for close was being called sync, now that we always do things async it changed the order of events. removing nextTick brings us back to that behavior
• src/gridfs/upload.ts
  • no longer relevant comment
• src/mongo_client.ts
  • maybeCallback connect - moved the floating function logic into the class, make TS happier and simplifies repition.
    • removed no mongos proxies found condition, this is unreachable, we removed this case in 3.x
  • maybeCallback close - this was mostly using promises already. topology and encrypter close is still wrapped though.
• src/operations/connect.ts
  • removed, see above
• src/sessions.ts
  • endSession, commit/abortTransaction async-ified.
  • promisified endTransaction, this one is a bit involved to convert since the finally vs handle the error is carefully part of correct transaction logic. should be done separately.
• src/utils.ts
  • Deleted maybePromise 🎉 🥳 🍾 🎂
  • changed the name of a variable so that there is no reference to maybePromise, definitelyPromise from here on out
• test/integration/collation/collations.test.js
  • this test was failing for a bit, fixed the capital
• test/integration/crud/aggregation.test.ts
  • added a beforeEachClient, and fixed the test the proved we were throwing synchronously ⚠️ This is no longer possible!
• test/integration/crud/explain.test.js
  • Explain demonstrates an exhaust cursor in one next call, so I had to debug a bug here, test got refactored in the process.
• test/integration/crud/misc_cursors.test.js
  • toArray and forEach do not throw on exhausted cursors, but .next and async iteration will, test needed debugging got refactored.
• test/integration/node-specific/cursor_stream.test.js
  • this test was hanging, the end event never came, I refactored but made one change to introduce a call to resume which is what I think was blocking the event. Before our sync call to callbacks would get us the event to emit even if the stream is paused, so this was just incorrect stream usage IIUC.
• test/integration/server-selection/readpreference.test.js
  • These tests were using sinon to check exact args passes to server selection, the args are slightly different but same logic is being checked.

What is the motivation for this change?

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: <type>(NODE-xxxx)<!>: <description>
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[baileympearson]

Looks really good overall, just some questions and minor comments

[baileympearson]

Can we annotate this function as throwing / add a comment? The error information used to be codified in the return type, but now it's lost.

[nbbeeken]

done!

[baileympearson]

Suggested change

// If a connection already been established, we can terminate early

[nbbeeken]

done