Prevent switching tabs while one of these blocks is glowing from
crashing because it is given a new ID.

eslint-plugin-import doesn't like these inline loaders.

I tried unsuccessfully to configure the recommended solution with `eslint-import-resolver-webpack`, but we should come back to this.

With this change we only use `xhr` in the `CostumeCanvas` component.

This way the instance can be reused, which allows access to non-deprecated `DataFormat` and `AssetType`.