Structure Support to NestedSDFGs and Python Frontend

[alexnick83]

Adds basic support for nested data (Structures) to the Python frontend. It also resolves issues with the use of Structures in nested SDFG scopes (mostly code generation).

NOTE: This PR handles only CPU code generation and fixes issues with libraries and transformations discovered during testing. It doesn't handle GPU/FPGA code generation, which will be studied in subsequent PRs.

[tbennun]

@alexnick83 there are two consistently failing tests in this PR (GPU).

[alexnick83]

@alexnick83 there are two consistently failing tests in this PR (GPU).

I don't see something in the PR that should directly cause these issues, but maybe the changes assisted in bringing to light pre-existing bugs.

Specifically, the adi test fails because __tmp62 and __tmp63 are not passed as arguments to the GPU kernels. The interesting thing here is that both of them have as original allocation scope the GPU kernel itself. However, the allocation scope changes to the corresponding State because they are placed in GPU global memory instead of registers. I will try to fix the argument passing (some other PR may have broken it), but we should look into fixing the storage types.

The conv2d test fails because the GPUAuto reduction expansion has some error. I confirmed this by disabling the expansion in the auto-optimizer to make it fall back to the CUDA (device) expansion. With the latter, the test passes. I will make a new PR to fix GPUAuto and disable the test for now.

Changes addressed