Check for method ID clashes across versions

[ernestognw]

Description

While researching patterns of access management, the solutions team identified a pattern of a contract that can dynamically create roles for functions in contracts, this means:

• There is a role manager contract
• contract Something is AccessManaged, ... can be also upgraded
• A subsequent upgrade can include a method that clashes with any of the previous EVM interfaces
• This would mean that a user with a role to access namely a function like foo() may clash with an upgrade to another function bar()
• This case will allow a user intended to use only foo() to also use bar()

[ericglau]

The goal of this issue will be to check for these kinds of function selector clashes between versions.

[frangio]

This check is different from the current checks because it makes an assertion about the history of a proxy. All current checks are purely assertions about a single contract's source code.

This is a significant difference that has design implications and efficiency implications.