Fix asset loader registration warning

[thepackett]

Objective

When registering and preregistering asset loaders, there would be a warn! if multiple asset loaders use a given extension, and an info! if multiple asset loaders load the same asset type. Since both of these situations are individually fine, it was decided that these messages should be removed.

Solution

Replace both of these messages with a new warn! that notes that if multiple asset loaders share the same asset type and share extensions, that the loader must be specified in the .meta file for those assets in order to solve the ambiguity. This is a more useful message, since it notes when a user must take special action / consideration.

[ghost]

I still think this should be hidden behind a feature, but there are many things that should be

[bushrat011899]

Simple change that resolves a problem I was facing earlier. Nice work!

[doonv]

This is great! This also fixes #11881.