ERC-6464 Multi-operator, per-token ERC-721 approvals.

StagnantERCcreated 2023-02-02requires ERC-165, ERC-721

Extends ERC-721 to allow token owners to approve multiple operators to control their assets on a per-token basis.

Authors: Cristian Espinoza (@crisgarner), Simon Fremaux (@dievardump), David Huber (@cxkoda), and Arran Schlosberg (@aschlosberg)

ERC-165 interface ids

Computed here as the XOR of the selectors each interface defines.

IERC6464 0x29b49ed2

`0x727ed55d`	`isExplicitlyApprovedFor(address,uint256)`	view
`0x92a2d6c9`	`revokeAllExplicitApprovals()`
`0xf6f383a8`	`revokeAllExplicitApprovals(uint256)`
`0x473de4c0`	`setExplicitApproval(address,uint256,bool)`
`0x78a6fa2e`	`setExplicitApproval(address,uint256[],bool)`

`0x095ea7b3`	`approve(address,uint256)`	ERC-721
`0x70a08231`	`balanceOf(address)`	ERC-721
`0x081812fc`	`getApproved(uint256)`	ERC-721
`0xe985e9c5`	`isApprovedForAll(address,address)`	ERC-721
`0x6352211e`	`ownerOf(uint256)`	ERC-721
`0xb88d4fde`	`safeTransferFrom(address,address,uint256,bytes)`	ERC-721
`0x42842e0e`	`safeTransferFrom(address,address,uint256)`	ERC-721
`0xa22cb465`	`setApprovalForAll(address,bool)`	ERC-721
`0x01ffc9a7`	`supportsInterface(bytes4)`	ERC-165
`0x23b872dd`	`transferFrom(address,address,uint256)`	ERC-721

Interfaces the spec defines alongside the core one, which an implementation may or may not carry.

0x390ff134 isApprovedFor(address,uint256)

Topic0 is the keccak256 hash of the signature, which is what a log filter matches on.

`0x4847355c152b0b1e3a552ce72358706bcfc55e5ebfe378c49560623a2347e7cb`	`ExplicitApprovalFor(address,uint256,bool)`
`0x2d7aeda3edd4aebdcd0ebd2ae8ff451ec174958cc035bf8b85d537e5375aa789`	`AllExplicitApprovalsRevoked(address)`
`0x7e87562dddf9f5613d1d4d2f67e65aedf9bc4bd832f075772ed965ba1117ba02`	`AllExplicitApprovalsRevoked(address,uint256)`