Asset3D:s constructors are named differently in C++ and Rust

[emilk]

In C++ we have from_file and from_bytes.
In Rust we have from_file and from_file_contents.

Basically we have two sources we care about:

• A file path
• The contents of a file

from_file_contents is very descriptive, so I think it winds out over from_byte.

from_file isn't great though - I could easily see someone be confused and pass a path to that (which I would not be surprised if it worked on some C++ compilers).

So I suggest we go with: from_file_path and from_file_contents.
Or shorten it to: from_path and from_contents.

Whatever we chose, we should pick the same for the new ImageEncoded.

We should also keep the old functions with a deprecation marker.

Python

In Python we use named arguments instead, and those are named path and contents, which I think are good, and go well with the suggested names.

[emilk]

We now have VideoAsset too, so high time to make this consistent