Keep in mind Buffer.toString() still exists, but returns [object Object].
Reason for removal of Buffer.toString() was that it implicitly used
TextDecoder with fixed "utf-8" encoding and no way to customize
the encoding.
This PR brings assertOps and assertResources sanitizers to Deno.test() API.
assertOps checks that test doesn't leak async ops, ie. there are no unresolved
promises originating from Deno APIs. Enabled by default, can be disabled using
Deno.TestDefinition.disableOpSanitizer.
assertResources checks that test doesn't leak resources, ie. all resources used
in test are closed. For example; if a file is opened during a test case it must be
explicitly closed before test case finishes. It's most useful for asynchronous
generators. Enabled by default, can be disabled using
Deno.TestDefinition.disableResourceSanitizer.
We've used those sanitizers in internal runtime tests and it proved very useful in
surfacing incorrect tests which resulted in interference between the tests.
All tests have been sanitized.
Closes #4208
