Inconsistent handling of HTTP redirects and file symlinks

[translatenix]

I just did some manual testing. Currently, Pkl handles HTTP redirects and file symlinks differently:

1. HTTP redirects: A program imports both https://example.com/bar.pkl and https://example.com/redirect-to-bar.pkl.

• Each import fetches/parses/evaluates the module separately.
• The resulting modules are incompatible. Their source code could be the same or different.
• Error and trace messages contain separate URLs.

2. File symlinks: A program imports both path/to/bar.pkl and path/to/symlink-to-bar.pkl.

• The module is fetched/parsed/evaluated only once.
• The resulting modules are compatible. They are the same module.
• Error and trace messages contain the URL of the import that was accessed first.

In other words: Files are canonicalized, HTTP URLs aren't. I think both should be.