feat: support import values from file: URI scheme

[ggreif]

I am suggesting importing amorphous files using the file: URI scheme:

import (blobby : Blob) = "file:Bla.wasm";
import (texty : Text) = "file:Bla.md";
import (principally : Principal) = "file:Bla.txt";

Leaving the type away would default to Blob.

To develop this idea further, import (friends : [{ name : Text; birthday : Text; ...}]) = "file:friends.csv" would be in reach. But I am sceptical of the utility (for other than test data generation).

Eventually resolves #4934.

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This is super early, I am butchering basically everything, such as

• type checker (T.Pre at bad phases)
• compilation units (there should be a ValueU)
• it should be file://
• use check_text

[ggreif]

This should be a type error

[crusso]

I think it might be easier to have differnt uris

impor bloby = "blob:Bla.wasm";
import texty = "text:Bla.md";
import principally = "principal:Bla.txt";
import envvar= "env:USER";
import foreignclass= "class:foo.wasm";