Indexed contracts store deployment block number immutably

[asaj]

h/t @yorhodes on #1907 (comment)

This would allow agents to index contract events optimally without any config beyond contract addresses.

[yorhodes]

contract Indexable {
    uint256 public immutable index = block.number;
}

[nambrot]

@asaj with the backwards cursor, do you still feel like this is valuable to change?

[avious00]

@yorhodes is this related to v3?