[DEMO] how we could replace specific token operations with the generic 2771 call proxy

[d10r]

Needed changes:

• Make SuperToken an IRelayRecipient, trusting the DMZForwarder
• Replace occurances of msg.sender with _msgSender() (which uses the 2771-encoded sender if present)

Here only SuperToken.increaseAllowance() was changed that way, with a new test case using it.

In order to do this, we'd need to

• use _msgSender() in all SuperToken methods
• mark the operationX methods as deprecated
• update SuperToken contracts

As long as there's SuperTokens not updated to this logic, we can't easily remove the then legacy operations types from batch call.
However we could remove the code from SuperToken if we conditionally re-map legacy operations in Superfluid.sol to use 2771Forwarder if the target token contract supports it.

[github-actions[bot]]

Changelog Reminder

Reminder to update the CHANGELOG.md for any of the modified packages in this PR.

• [ ] CHANGELOG.md modified
• [ ] Double check before merge

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 87.99%. Comparing base (0b33f76) to head (8e6a20a).

Files with missing lines	Patch %	Lines
...reum-contracts/contracts/superfluid/SuperToken.sol	80.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## supertokenlib-iteration #2035 +/- ## =========================================================== - Coverage 88.00% 87.99% -0.02% =========================================================== Files 108 108 Lines 6768 6779 +11 Branches 974 974 =========================================================== + Hits 5956 5965 +9 - Misses 810 812 +2 Partials 2 2 ``` | [Flag](https://app.codecov.io/gh/superfluid-finance/protocol-monorepo/pull/2035/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=superfluid-finance) | Coverage Δ | | |---|---|---| | [ethereum-contracts](https://app.codecov.io/gh/superfluid-finance/protocol-monorepo/pull/2035/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=superfluid-finance) | `94.15% <83.33%> (-0.05%)` | :arrow_down: | | [sdk-core](https://app.codecov.io/gh/superfluid-finance/protocol-monorepo/pull/2035/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=superfluid-finance) | `87.99% <83.33%> (-0.02%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=superfluid-finance#carryforward-flags-in-the-pull-request-comment) to find out more.

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[d10r]

note: BaseRelayRecipient._getTransactionSigner() does not do what it's natspec claims.