Change tokenURI field of ERC20WithMetadata from private to internal

[leonprou]

🧐 Motivation
I want to use ERC20WithMetadata contract, but I would like to introduce logic that changes the tokenURI field. For example that just the owner of the token can change the tokenURI.
We are building a token studio, and the issuer might be unsure about token metadata when he creates the token. Also some token metadata like addresses and etc might change. Not sure, but I think it doesn't break the EIP-1047.

📝 Details
Changing the tokenURI field to internal should solve this problem.

[nventuro]

EIP721 explictly allows this (see the Rationale section, under 'Metadata Choices':

The URI MAY be mutable (i.e. it changes from time to time). We considered an NFT representing ownership of a house, in this case metadata about the house (image, occupants, etc.) can naturally change.

I think this is a fair point and wouldn't be against this addition.

[leonprou]

@nventuro great, thanks for the quick response.

I guess it will take some time this will be released. So for now I copied the TokenMetadata contract and make the change myself. You can see it here.

Also I can make a PR to the repo if it helps.