Loader GetURL incorrectly handles file:// absolute URLs, breaking resource loading and Spine atlas page image loading

[aomsir]

Description

When running Phaser under the file:// protocol (no local HTTP server),
the Loader incorrectly treats absolute file:// URLs as relative.
As a result, baseURL is prepended to them, producing an invalid
combined URL.

This issue affects:

1. Manual resource loading using file:// URLs
2. Spine atlas loading, because page images inside a .atlas file
   often include absolute file:// paths
   • Phaser automatically loads these image URLs\
   • Loader misinterprets them\
   • Resulting URL becomes invalid → image fails to load

Example of incorrect behaviour:

baseURL: file:///Users/me/project/
file.url: file:///Users/me/project/assets/spineboy-pma.png

Result:
file:///Users/me/project/file:///Users/me/project/assets/spineboy-pma.png

This happens because GetURL() does not classify file:// as an
absolute URL, unlike http(s)://, blob:, data:, etc.

Reproduction

1. Basic resource load

this.load.setBaseURL("file:///Users/me/project/");

this.load.image("pic", "file:///Users/me/project/assets/img.png");
// Incorrect: baseURL is prepended to an already absolute file:// URL

2. Spine atlas loading

Inside spineboy.atlas:

file:///Users/me/project/assets/spineboy-pma.png

Phaser automatically loads the page image referenced in the atlas.
But because the URL starts with file://, Loader incorrectly prefixes
baseURL, producing an invalid URL → page image fails to load.

Expected behaviour

• file:// URLs should be treated as absolute (same as
  http/https/blob/data).
• Loader should not prepend baseURL to them.
• Spine atlas auto-loading should correctly load page images
  referenced with absolute file:// URLs.

Affected versions

Phaser every version

Related PR

Fix PR: #7210