Compare upgrades in slither.utils.upgradeability

[webthethird]

Based on @montyly's recommendation re: adding what I had been doing in my diff_with_v2.py directly within Slither, instead of as a new upgradeability check.

This adds a new slither.utils.upgradeability containing a function compare(v1: Contract, v2: Contract), which returns a dictionary of lists of Variables/Functions, and a helper function is_function_modified(f1: Function, f2: Function), which returns True if the function is modified or False otherwise.

The dictionary returned by the compare function has the following lists:

{
    "missing-vars-in-v2": list[Variable],
    "new-variables": list[Variable],
    "tainted-variables": list[Variable],
    "new-functions": list[Function],
    "modified-functions": list[Function],
    "tainted-functions": list[Function]
}

In this context, a tainted variable is a preexisting variable which is read or written by a new or modified function, and similarly a tainted function is an unmodified function that calls a modified function.

I made sure to address the feedback he gave me:

• You need to check of immutable here
• An issue with the comparison with get_summary, is that it might miss a change in the logic of the function. Like if a condition is inverted for example. One thing that we could use is function.source_mapping.content_hash , this returns an hash for the function source code. So if the source code differ you can detect it. It’s fast, however a downside is that if there is a change in a name, or in a comment, it will lead to a false positive. A better approach would be to compare the CFG of the two function; because we are looking for strict equivalence here, it should not be too difficult to do. Even a naive approach to walk through the CFG and compare the IR opcode should give good result I think.

[webthethird]

This was blocked by a bug in the CI tests, but all checks are passing now

[webthethird]

This is now included in PR #1757