Allow Ownable to work with meta-trasnactions (ERC2771Context)

[drortirosh]

The following code fails to compile:

  import "@openzeppelin/contracts/metatx/ERC2771Context.sol";
  import "@openzeppelin/contracts/access/Ownable.sol";

  contract MyContract is ERC2771Context, Ownable {
  
    constructor(address forwarder_) 
      ERC2771Context(forwarder_) {
    }

The error:

TypeError: Immutable variables cannot be read during contract creation time, which means they cannot be read in the constructor or any function or modifier called from it.
  --> @openzeppelin/contracts/metatx/ERC2771Context.sol:18:29:
   |
18 |         return forwarder == _trustedForwarder;
   |                             ^^^^^^^^^^^^^^^^^

The reason for this problem, is that Ownable attempt to set the owner, and uses _msgSender() in its constructor.
However, this fails to compile, since it is forbidden to access members from a constructor code (the trustedForwarder address)
Luckily, it is OK to use the normal msg.sender in this case, since a constructor call can't be called directly through meta-tx anyway..

Fixes #????

PR Checklist

• Tests
• Documentation
• Changelog entry

[Amxx]

WOW, thank you for this finding @drortirosh.

This is a serious issue that we will try to address quickly!