feat[next][dace]: Fix GTIR-to-SDFG lowering for failing tests

[edopao]

This PR addresses some problems encountered during GTIR/DaCe integration.

• Handle field size symbol as explicit scalar argument
• Support SDFG positional arguments (not only keyword arguments)
• Use explicit subset on source node for target write
• Add test case for copy from one field to itself using an explicit domain subset
• Extend test case with cond by using an expression on scalar arguments as if-statement

[havogt]

Looks good to me.