Custom Errors For ERC20 and unit tests

[lhemerly]

Fixes #2839

Add feature custom error to ERC20

Testing is raising errors for multicall, ERC777 and ERC 4626 because I have not added the feature to them yet, and they are using ERC20 behavior. Wanted to make sure the design decisions I made for the feature and testing are OK so I can move forward to the other contracts

• [ X ] Tests
• Documentation
• Changeset entry (run npx changeset add)

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[ernestognw]

Hey @lhemerl, thanks for the contribution.

For context, EIP-6093 was published for community feedback before we implement it into OpenZeppelin Contracts for the following reasons:

1. We don't want to make arbitrary decisions on the way custom errors should look, and we're rather asking for feedback (this is the official discussion)
2. We'll try to use the same rationale in 6093 for migrating all the contracts in 5.0
3. Making the changes as of now will be breaking for the library as stated in our API Stability docs

Also, we'll deprecate ERC777 in 4.9 so the testing issues on it can wait.

I'll close since it's too soon for 5.0 changes, but feel free to join the 6093 conversation, especially if you saw any particular use case we didn't consider while you were working on this.