Fix immediate nested loaded assets not loading their dependencies.

[andriyDev]

Objective

• Previously if you loaded an immediate nested asset, it would not load any of its dependencies. This means that you could have handles in your asset that would never load.
• Fixes Dependencies of immediately loaded nested asset never start loading. #20988

Solution

• Propagate loading dependencies to immediate asset loads.
• I also deduped some test App setup code.

Testing

• Added a test.

One case that does have a slightly undesirable effect is when you immediately-load an asset, take some data from it (but no dependency handles), and then drop the immediately-loaded asset. This change will now also initiate a dependency load, even though we won't use it.

However, A) it is much more surprising to have a handle that will never be loaded, B) we should end up cancelling the dependency load once we drop the handle, so we shouldn't pay too much of the cost of loading.