dev: enable rule warn no-floating-promises and no-misused-promises

[marksvc]

The rules are not enabled for spec and stories files. It may also be
useful to have the rules on in those files, but (1) calls to async
methods in fakeAsync do not need awaited, and (2) the IDE understands
toBe, toEqual, etc to return Promises.

Ideally the rules would mark occurrences as errors, but there are many
occurrences that first need to be cleaned up.

---

This change is 

[marksvc]

This PR turns on eslint warnings for rules no-floating-promises and no-misused-promises.

Consider this code:

async myMethod(): Promise<void> {
  mkdir('/data');
  await writeFile('/data/hello.txt', 'Hello, world!');
}

The call to async function mkdir might not finish before the call to writeFile starts. Rule "no-floating-promises" flags this so you notice that you should await mkdir.

Or consider this code,

async function risk(): Promise<void> {
  throw new Error("Problem!");
}

async function click(): Promise<void> {
  try {
    console.log("Trying something!");
    risk();
  } catch (e) {
    console.log("It was a problem!");
  }
  console.log("Phew!");
}
await click();

When this code runs, will it print "It was a problem!"? Nope! You need to await risk and then the exception will be handled.

Consider this code:

async click(): Promise<void> {
  navigate('/destination');
}

Some calls to async methods might not be important to await. You fire it and it will happen when (and if) it happens. You can prefix void to the call to specify that you intend to call an async method, without awaiting it, and without handling any exceptions that happen. For example, void navigate('/destination');

Our codebase has a lot of these occurrences, so I am having eslint mark them as warnings rather than errors.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.59%. Comparing base (4d3a87c) to head (76c0c54).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3391   +/-   ##
=======================================
  Coverage   82.59%   82.59%           
=======================================
  Files         608      608           
  Lines       35966    35966           
  Branches     5842     5842           
=======================================
  Hits        29705    29705           
  Misses       5399     5399           
  Partials      862      862           

☔ View full report in Codecov by Sentry.
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[pmachapman]

So many warnings!

The warnings I investigated looked like they were intended by the developer to be floating or misused.

I'd be interested in getting wider consensus/feedback form the team before merging. Should we discuss this in the planning meeting tomorrow?

@pmachapman reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @marksvc)

[marksvc]

Sounds good.