The TS compiler is likely to test paths with extensions and try to
load them as files. Therefore `fileExists()` and methods that rely
on it need to be able to distinguish between real files and directories
that have paths that look like files.
This came up as a bug in ngcc when trying to process `ngx-virtual-scroller`,
which relies upon a library called `@tweenjs/tween.js`.
PR Close#31289
d171006083