This fixes a few error surfaced by adding `"strict": true` to `tsconfig.json`.
* `_callFs(fs.readdir, /* ... */)` needs explicit types because `fs.readdir` has a few overloads, which was confusing type inference.
* `TempScopedNodeJsSyncHost._sync` is an uninitialized property, but it was already being checked for `undefined`, so I simply made its type optional.
* `TempScopedNodeJsSyncHost.files` had an incorrect type assertion, but was otherwise correct. I just removed the assertion and let type inference do the trick.
It is unused within our code, as webpack will do the file watching.
This removes 1.4 MB from the download size of the package.
See https://codepen.io/alexeagle/full/zbZWRM
BREAKING CHANGE:
Users who rely on angular-devkit/core to do the file watching must add chokidar to their devDependencies.
