* fix: allow event loop to process during wait queue processing

Running `processWaitQueue` on the next tick allows the event loop
to process while the connection pool is processing large numbers of
wait queue members. This also uncovered a few issues with timing
in our tests, and in some cases our top-level API:
  - `commitTransaction` / `abortTransaction` use `maybePromise` now
  - `endSession` must wait for all the machinery behind the scenes to
     check out a connection and write a message before considering its
     job finished
  - internal calls to `kill` a cursor now await the the process of fully
    sending that command, even if they ignore the response

NODE-2803

Uses a primary read preference for write / DDL operations, needed for server selection.

NODE-2784

The logic for waking the AsyncInterruptibleInterval sooner than its
interval is dependent on an ability to reliably mark the last call
made to the wrapped function. In environments like AWS Lambda where
instances can be frozen and later thawed, it's possible for the
last call to be in a distant past even though the internal timer
has not completed yet. This change ensures that we immediately
reschedule in these situations.

NODE-2829

Update ESLint and bring in a modified version of our config from 4.0. 
ESLint manages running and checking prettier formatting. 
Update mocha and bringing in the config from the 4.0 branch.

Update connection-monitoring-and-pooling tests
ensuring ConnectionCreated proceed ConnectionReady events.
Add spec sync script.

NODE-2804

Revet mocha upgrade due to nodejs version requirements.
Correct client_encryption test filter to operate as expected on nodejs v4.

NODE-2832

NODE-2834

NODE-2807

NODE-2788

NODE-2827

NODE-2172

NODE-2851

A connection could potentially be leaked if a wait queue member was
cancelled (due to timeout) before execution. In these cases we
should return the connection back to the list of connections for
future use or pruning.

NODE-2865

Some package managers such as yarn or pnpm require strict definitons
of project dependencies which does not play well with our `require_optional`
approach to peer optional dependencies. This change utilizes a relatively
new `peerDependenciesMeta` field to inform these package managers of 
these optional dependencies.

NODE-2867

A new KerberosClient should be made for each individual authentication
attempt, rather than the current approach which creates one and shares
it for all attempts.

NODE-2859

We make an implicit assumption with our default socket timeout that
most operations will complete within the current default of 5min. This is
not the case for services like Atlas Data Lake, which may regularly take
far longer to complete operations. In general we can't make any
assumptions about how long an operation will take to complete, and so
the default socket timeout is now 0 (infinity) unless otherwise indicated.

NODE-2835

A performance regression was identified in switching the connection
pool to using setImmediate instead of process.nextTick for wait
queue processing. This patch reverts that change.

NODE-2861

A typo resulted in a provided username not being properly assigned to the command
send to the server when using X509 authentication.

NODE-2869