feat[next][dace]: GTIR-to-SDFG lowering of cast_ builtin

[edopao]

Add support to lower GTIR like:
y @ c⟨ IDimₕ: [0, size) ⟩ ← as_fieldop(λ(a) → cast_(·a, float64), c⟨ IDimₕ: [0, size) ⟩)(x);

Test case added.

[havogt]

did you intentionally remove the copy test?

[edopao]

did you intentionally remove the copy test?

Yes, the test was not useful because it used as_fieldop to do element-wise copy of the field. Besides, in #1609 I will introduce another kind of copy test which covers an interesting corner case of lowering to SDFG.