Meta Issue: 4.5

[frangio]

Candidates:

• Add SignedMath with math utilities for signed integers #2686
• Re-enable immutable forwarder in ERC2771Context #2917
• Extend MerkleProof to support unsorted Merkle tree #2815
• Fix memory leak in merkle verification #3039
• Add Base64 library to utils #2884
• Simplify UUPSUpgradeable along the lines of ERC1822 #3021
• Initializer must be reusable for upgrade Initializers #2901
  • Blocked by change in type (bool → uint8) that is not supported by the upgrades plugin
  • Postponed to 4.6
• Use invalid opcode to consume all gas in MinimalForwarder #3035
• Implement Non Fungible Token Royalty (EIP2981) #3012
• Bump ERC1967 pragma to 0.8.4 #3036
• Update pragma for Address.sol util to ^0.8.1 upwards #3031
• Governor
  • Add the possibility to include ERC721 token voting within OZ Governor module  #2873
  • Add a relay mechanism in the governor #2926
• Make more functions virtual #3078
• Do not reduce approval on transferFrom if current allowance is type(uint256).max #3085
• Fix encoding of signature+calldata in GovernorCompatibilityBravo #3100

[Amxx]

To cherry-pick (fixed during RC)

• Move abs(int256) from Math to SignedMath #3110
• Fix broken pull request links in change log #3114
• Make royaltyInfo(uint256 _tokenId, uint256 _salePrice) virtual #3133
• Fix typo in CHANGELOG #3135
• Add a _spendAllowance function to ERC20 & ERC777 #3170 (and Rename some ERC20 parameters to match the standard document. #3167 to avoid conflicts)

[frangio]

4.5 is now released!