Gd/ssa arrays

[guipublic]

Support for Arrays in the SSA form.

• Only static arrays (i.e fixed length and constant indexing) are supported for now.
• Arrays are treated as a chunk of memory, access to the array is translated into accessing the memory.
• Array objects are represented with the Pointer type, for equality check or constraints and function parameters or return type.

Static access to the memory is optimized via the use, when reading the memory, of a mapping of addresses to their stored values. Overflow strategy uses this mapping when possible and also maintains a maximum value of the array (for the case when the mapping does not exist).
CSE put all read/write operations in the same anchor but uses a different one for each array. It is checked in reverse order so that most recent write operation kills the rest of the anchor.

In summary, the changes are mainly around these files:

1. mem.rs: define a virtual memory containing arrays
2. node.rs: new Pointer type which references an array. New Constrain operator to implement distinct and equal constraints
3. code_gen.rs (parse AST): generate read and write instructions (there is no ssa value for the arrays as any write would invalidate the whole array)
4. optim.rs (CSE): remove redundant memory access (e.g 2 consecutive reads or two consecutive writes)
5. integer.rs (overflow): map static writes to their values to retrieve the maximum values of a read.
6. acir_gen.rs (ACIR): map static writes to their values to retrieve relevant witnesses for read operations. Implement equality checks and constraints using predicates.

[jfecher]

Looks mostly good, some style/naming suggestions mainly.

[jfecher]

LGTM!