Named arguments can be used in mapping types in ERC20

[allwin199]

🧐 Motivation

openzeppelin-contracts/contracts/token/ERC20/ERC20.sol

Lines 39 to 41 in d6b63a4

	mapping(address => uint256) private _balances;
	mapping(address => mapping(address => uint256)) private _allowances;

📝 Details
The Above lines can be changed to this.

mapping(address owner => uint256 value) private _balances; 

mapping(address owner => mapping(address spender => uint256 value)) private _allowances; 

[allwin199]

I am open to contributing.

[Amxx]

This is already addressed by #4433

[Amxx]

Duplicate of #4343

[allwin199]

oh sorry! didn't notice.