auto create imported asset folder if needed

[mockersf]

Objective

• Since Don't auto create assets folder #11218, example asset_processing fails:

thread 'main' panicked at crates/bevy_asset/src/io/source.rs:489:18:
Failed to create file watcher: Error { kind: PathNotFound, paths: ["examples/asset/processing/imported_assets/Default"] }

start from a fresh git clone or delete the folder before running to reproduce, it is in gitignore and should not be present on a fresh run

bevy/.gitignore

Line 18 in a657478

imported_assets

Solution

• Auto create the imported_assets folder if it is configured

[mockersf]

In other words, instead of what was done previously, where file system control was given to the reader, should it be given to the writer instead?

That would result in the same situation as before #11218, and the assets folder created when not needed

[TheoDulka]

Ahhh yeah of course, somehow misunderstood FileAssetWriter::new to be the file initializer, instead of it setting the base path of the writer, so it would end up creating the assets folder. I'll delete the question

[nvdaz]

Tried it and looks good.

Asset processing ideally shouldn't need file_watcher to work (so it's portable), but that's a separate issue.