Standardize fetch calls to `file:` URLs

[ovflowd]

Pretty much a X-Post from @aduh95's original issue: WinterTC55/fetch#5, there's still relevancy in supporting the file:// protocol on fetch.

[ovflowd]

Relevant threads:

• fetch: Enable fetch via file URL (under flag) nodejs/undici#2751
• Standardize fetch calls to file: URLs fetch#5
• [experimental fetch] Allow fetching file:// urls nodejs/node#42003