WIP: Vector Improvements

[ncough]

A bunch of changes I have been meaning to push up, cleaning up the vectoriser to deal with almost everything under aarch64_vectors*. Placeholder for me, as it really needs to be broken up into a series of PRs, when I get around to it.

General bug fixes:

• Fix take and drop list utilities.
• Fix CSE to not consider expressions over mutable variables as candidates for elimination. The introduction of the CSE variable may not be correctly placed with respect to any mutation of these variables.
• Fix dead code removal to not remove impure function calls, as they may mutate global state.
• Improve type checking for post partial evaluation to handle arrays and global variables.
• At some point sdiv_int worked its way into the code base, but it doesn't exist.

Improved coverage testing of vectors:

• Initialise the _Z array with random values to get some results out of coverage testing for vectors instructions.
• New fp operations FPRSqrtEstimate and UnsignedRSqrtEstimate are now reachable, add them to the inlining config.
• Extend the interpreter to support an integer bit slice update. Haven't added this to the partial evaluator.
• Add an implementation of sqrt_real, not sure if it's accurate to hardware though.

Change our primitive shift operations to line up with SMTLIB:

• Shifts now take an unsigned bitvector to represent the shift amount, and both the shift and value are of the same width.
• Support a primitive for rotate operations, as requested by Improving Rotation Translation #83
• This changes the signature for shifts, so downstream uses have to be updated.

Changes to simplify and improve the vectoriser:

• Move all vectoriser related logic to a new file, libASL/loops.ml.
• Break out the induction variable substitution into a pre-pass that is applied before IntToBits, so that it can reason over trivial integer operations.
• Handle vectorisation with a series of primitive classes and common logic to transform each class.
• Move vector expression cleanup to a post-phase.
• Keep select_vec and update_vec operations in terms of integer positional arguments until the last possible phase, to simplify reasoning.
• Building on these simplifications, add a series of vectorised floating point operations and new reductions.
• This changes the signature for some vector operations, so downstream uses have to be updated.

Remaining:

• Init the entire _Z array with random values, rather than just the low 64-bits.
• Find out what sqrt_real should be.
• Add integer bit slice to partial evaluator (Maybe? Doesn't seem to come up outside of fp prims).
• Add missing floating point operations to override.asl.