Add custom paths support (custom res:///user://-like paths)

[adamscott]

tl;dr

Enables custom resource paths that users can setup and use themselves.

# Maps a path to a custom path
FileAccess.map_path_to_custom_path("home", "/home/myself")
# (with or without the ://, it removes it automatically)
FileAccess.map_path_to_custom_path("home://", "/home/myself")
# Map classes (custom `FileAccess` and `DirAccess`) to custom path
FileAccess.map_classes_to_custom_path("cloud://", "CloudFileAccess", "CloudDirAccess")
# Removes a custom path
FileAccess.remove_custom_path("home")
# Checks if the prefix is supported
FileAccess.is_custom_path("home")
# Returns a dictionary containing the definition of the custom path
FileAccess.get_custom_path_data("home")
# Returns an array containing all the custom path prefixes
FileAccess.get_custom_paths()

Todo

•  Write the documentation

Fixes

• Fix Implement custom resource path support godot-proposals#6307
• Closes godotengine/internal-team-priorities#92

[arkology]

This is big step (even if not directly) towards global addons 🥳
I like it

[adamscott]

This is big step (even not directly) towards global addons 🥳

That's the goal!

[RedMser]

Why do is_resource_path and get_resource_path(s) fail for res and user? I understand that adding/removing them is dangerous, so those erroring makes sense.
But the current handling of the getter methods are just exposing an implementation detail to the user. They should instead be a consistent API for "every virtual path *:// managed by Godot"...

[adamscott]

But the current handling of the getter methods are just exposing an implementation detail to the user.

No, user:// and res:// are special cases handled differently. This PR is not about exposing an implementation detail, it's a feature in itself.

[zedrun00]

the pr is good.
i used the pr, i think will need add prefix_dir options in "EditorFileDialog" and "FileDialog"

[CycloneRing]

@adamscott Do you think it's possible to add memory based file system to this PR? A simple VFS so files can be used directly from memory like "memory://my_scene.tscn"

[adamscott]

@adamscott Do you think it's possible to add memory based file system to this PR? A simple VFS so files can be used directly from memory like "memory://my_scene.tscn"

This clearly isn't in the scope of my PR.

[nonchip]

@adamscott are you sure? it is in the scope of your PR's example usage, so i would say the answer is "already possible, no need to add anything".

FileAccess.map_classes_to_custom_path("cloud://", "CloudFileAccess", "CloudDirAccess")

[scgm0]

@adamscott Do you think it's possible to add memory based file system to this PR? A simple VFS so files can be used directly from memory like "memory://my_scene.tscn"

This? #98287