fix: Compute the correct slice length when coercing from a literal array of complex types

[ggiraldez]

Description

Problem*

Resolves #4967

Summary*

There is a problem in the array to slice coercion code. When evaluating the coercion, it does not take into account that for SSA, complex types such as tuples and structs are flattened, resulting in an array representation with length of elements times the size of the complex type (as a result of the flattening). This results in the replacement slice having an incorrect size.

Then, because the slice has an inflated size, the code which decodes the elements of the slice for printing or tracking (in the debugger) crashes when it attempts to decode beyond the values that it has available.

Additional Context

There are two additional minor changes introduced in this PR:

1. Removed the Optional<> for PrintableType::Array's length. This was introduced to be able to print slices (setting the length to None), but those are now represented properly with PrintableType::Slice.
2. Added support for printing slices.

Both are pretty small changes which I made while investigating the issue, but I'm willing to send separate PRs for those if required.

I also expanded the existing test cases to verify both the coerced slice length and printing of slices.

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions]

Thank you for your contribution to the Noir language.

Please do not force push to this branch after the Noir team have started review of this PR. Doing so will only delay us merging your PR as we will need to start the review process from scratch.

Thanks for your understanding.

[vezenovm]

Thank you for this!