Check for initializer errors

[ericglau]

Draft PR to detect issues in parent initializer calls.

This infers functions as initializers if they have a modifier that is initializer, reinitializer, or onlyInitializing, or the function itself is named as initialize, initializer, reinitialize, or reinitializer.

This reports an error if any parent contract has an inferred initializer and any of the following are true for the (child) contract being validated:

1. Missing initializer: This contract does not appear to have an initializer.
2. Missing initializer call: This contract's initializer is missing a call to a parent initializer.
3. Duplicate initializer call: This contract has duplicate calls to the same parent initializer function.
4. Incorrect initializer order: This contract does not call parent initializers in the correct order.

Limitations:

• This does not recursively check the initializer function, where its called functions may have calls to the parent initializer. This could result in a false positive, but users could workaround this by using unsafe-allow missing-initializer-call

Questions:

• Should we enable this feature by default or make this opt-in (at least for now)? This could cause unexpected errors if users' contracts do not follow our convention. For example, if a parent contract has an initialize function that has nothing to do with proxy initialization.

Remaining:

• Resolve the above question, and fix the tests to avoid these errors in unrelated test cases.
• Add a way to ignore all initializer errors from options
• Documentation
• Improve error messages to include more context, such as what was the expected linearization order and what was found instead, or what the duplicate call was
• Improve error messages to have more detailed suggestions for user action.
• Update changelog and bump version

Fixes #160