Vector as output

[segfault-magnet]

We've had a meeting with the compiler team where we agreed to the following:

• When returning or logging, vectors cannot be nested in other types.
• retd will be used to return vector data -- i.e. vector elements will be contained in the ReturnData receipt.
• logging a vector will log its elements.

Currently, we've adapted the SDK to throw a compile-time error if it detects the usage of vectors in the output type of a contract method.

If somebody should circumvent that and call ABIDecoder::decode... on a vector or a type containing one, the SDK will panic with an appropriate message.

Blocked -- waiting for support from the compiler.

Related:
FuelLabs/sway#2900
#600

[iqdecay]

Part of this issue is this one: #746

[iqdecay]

Solved by #848 (I am going to add support for logging vectors because I didn't think of it at first)

[iqdecay]

Solved by #848.
Vector logging is tracked in #898