Asset per file scheme, stage 1

[Imberflur]

This is "stage 1" in converting bauble to a file per top level asset scheme.

Additionally there are changes to support having our bauble editor work with local assets instead of inline assets.

Asset per file

If an object appears first in the file and its name matches the file's name, its path will now be simplified to the path of the file. Additionally, the object will be marked as top_level (via a new field on Object and as a property available on assets in PathReference).

Custom naming for additional objects

We add AdditionalUnspannedObjects::new_with_custom_namer. AdditionalUnspannedObjects is used when creating new values that need to also create additional objects that they reference. This new method allows custom names instead of creating all new referenced objects as inline sub-objects.

Misc changes

Removed newline at the beginning of display_formatted output and added a newline at the end. Now files generated with this will have a trailing newline.

Exposed constant used for the builtin Ref type's path so external code can reliably identify the builtin Ref type.

[MavethGH]

When and why do we append that type id number?

[Imberflur]

This is done in here

bauble/bauble/src/value/convert.rs

Line 1064 in 1210f4f

TypePathElem::new(format!("{}&{}", meta.object_name, ty.inner()))

and here

bauble/bauble/src/value/convert.rs

Line 427 in 1210f4f

let name = TypePathElem::new(format!("{}&{}", self.object_name, ty.inner())).unwrap();

The reasoning I have seen in documentation in our editor code is:

/// These sub-objects will have some path like `path::to::root::object&23&34@0`. The numbers are
/// there to give sub-objects more unique names to make hot-reloading assets better. And are based
/// on the types of the object. And the number `@0` at the end is there to make sure the name is unique.

I think it basically somewhat alleviates the issue that an array, optional field or similar, could effect the names of sub-objects in all following fields when an item is added/removed. I say "somewhat" because if the sub-objects across fields had common types then this would not change anything.