Extend file system provider interface

[msujew]

Extends the file system provider to have the common file system operations:

1. Reading text file
2. Reading directory
3. Reading binary file
4. Checking whether a file exists

Both of these are now available in their respective sync and async versions. However, the framework itself exclusively uses the async methods. The sync method is available for adopters.

This change required to update the @types/node dev dependency to 18, as the Buffer class only started to correctly subtypethe Uint8Array class during that release.

[msujew]

cc @cdietrich I believe you were interested in sync fs methods, right?

[cdietrich]

yes

[spoenemann]

Since the new interface methods are not optional, we should regard this as a breaking change.