BREAKING(media-types): rename extensionsByType to allExtensions

[kt3k]

This PR renames extensionsByType to allExtensions to align the naming convention to extension which takes the same arguments.

What's changed

extensionsByType has been renamed to allExtensions

Motivation

extension and extensionsByType take the same arguments (the content type), but named in an inconsistent way. This change align the naming of the latter to the former.

Migration

-import { extensionsByType } from "@std/media-types";
+import { allExtensions } from "@std/media-types";