feat: add designated caller on token portal and update uniswap to use it.

[rahul-kothari]

Description

Fix #877 -> currently, anyone can call our token portal to consume the withdraw message. This doesn't seem a problem there is no use of msg.sender in its code and the funds would go to the recipient specified in the message hash. However, in some cases it might be important, like when a contract is consuming multiple messages as part of a smart contract function - in such a case only this contract should call it.

Note - once again we implement this at the portal and not the protocol side to maintain flexibility.

I have added tests in solidity to check that caller works as expected.

This builds on #876 which I will fix after this pr! There I will add more tests on an e2e scale.

Checklist:

• I have reviewed my diff in github, line by line.
• Every change is related to the PR description.
• I have linked this pull request to the issue(s) that it resolves.
• There are no unexpected formatting changes, superfluous debug logs, or commented-out code.
• The branch has been merged or rebased against the head of its merge target.
• I'm happy for the PR to be merged at the reviewer's next convenience.