Fix validators public key aggregation

[waymobetta]

Description

As explained in the related issue, the current APK (aggregated public key) is constructed by pulling in validator data from the validators who were selected for the current epoch, taking their public keys, then aggregating them.

Instead, the APK should be constructed by fetching all validators from the pool of validators for the epoch and then applying the bitmap included in the Istanbul extra data stored within the block header against this validator list. Once this filtering is done, then can the APK be constructed to appropriately represent the block that was verified.

This resulting list of validators will be only the validators who signed the block, rather than the entire pool of validators who were selected for the epoch.

---

Note:

• chain/listener/listener.go has code added for debugging purposes
• validatorsync/syncerstorr.go also has some logs added for debugging purposes
• validatorsync/syncerstorr_test.go needed an additional argument because of the change to GetAPKForBlock
• validatorsync/sync_test.go needed an additional argument because of the change to GetAPKForBlock

_The additions to the syncerstorr_test and sync_test did not themselves break the tests; the tests were found to be failing prior to the change. This is being investigated_

Related Issue Or Context

Closes: #116

How Has This Been Tested? Testing details.

Unit tests were written.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation

Checklist:

• [x] I have commented my code, particularly in hard-to-understand areas.
• [x] I have ensured that all acceptance criteria (or expected behavior) from issue are met
• [ ] I have updated the documentation locally and in chainbridge-docs.
• [x] I have added tests to cover my changes.
• [ ] I have ensured that all the checks are passing and green, I've signed the CLA bot

[github-actions[bot]]

Go Test coverage is 41.1 %\ :sparkles: :sparkles: :sparkles:

[github-actions[bot]]

Go Test coverage is 41.1 %\ :sparkles: :sparkles: :sparkles: