[ABC-495] Get an overview of curves' attribute data

[SanaJal]

Purpose of this PR

Ticket/Jira #: ABC-495 & ABC-486

• [ABC-495] : This PR gets an overview of the attributes (for now : name and size) and store them
• [ABC-486] :This PR gets the number of attributes so that we know by how much to resize the array that will contain the attributes

Testing

Manual testing. Add a curve alembic asset with attributes, you can add these lines to facilitate the debug in AlembicCurvesElement.cs around line 47:

       // to test
           string name = Marshal.PtrToStringAnsi(curves.attributesSummaryList[0].name);
           Debug.Log("name: " + name);

You can also inspect it using breakpoints.