AMF Loader should preserve part names

[EnricSala]

I am exporting a CATIA model with multiple parts to a single AMF file, which is useful because it avoids having to load multiple files.

The problem is that when loading an AMF file with multiple parts, they lose their assigned part name, making it difficult to identify the parts to apply dynamic changes to them.

Sample AMF file with part names:

<?xml version="1.0" encoding="utf-8"?>
<amf unit="millimeter">

    <metadata type="name">MODEL_NAME</metadata>

    <object id="1">
        <metadata type="name">PART_1_NAME</metadata>
        <mesh> ... </mesh>
    </object>

    <object id="2">
        <metadata type="name">PART_2_NAME</metadata>
        <mesh> ... </mesh>
    </object>

</amf>

It would be very helpful if the part names were preserved when loading AMF files.

See submitted PR #9215.