feat: add deploy permit2 util (Uniswap#187)

For folks building on top of permit2 it's kinda annoying to have to use
viaIR just becuase permit2 uses viaIR. This commit adds a test utility
that they can import to deploy permit2 from precompiled bytecode to
avoid needing to recompile it on their end

.gas-snapshot

@@ -34,6 +34,9 @@ AllowanceUnitTest:testUpdateAllRandomly(uint160,uint48,uint48) (runs: 256, μ: 4
 AllowanceUnitTest:testUpdateAmountExpirationRandomly(uint160,uint48) (runs: 256, μ: 39224, ~: 39225)
 CompactSignature:testCompactSignature27() (gas: 253)
 CompactSignature:testCompactSignature28() (gas: 141)
+DeployPermit2Test:testAllowanceTransferSanityCheck() (gas: 101958)
+DeployPermit2Test:testDeployPermit2() (gas: 4337486)
+DeployPermit2Test:testSignatureTransferSanityCheck() (gas: 92819)
 EIP712Test:testDomainSeparator() (gas: 5804)
 EIP712Test:testDomainSeparatorAfterFork() (gas: 10787)
 MockPermit2Lib:testPermit2Code(address):(bool) (runs: 256, μ: 3016, ~: 3016)

README.md

@@ -26,6 +26,20 @@ The `AllowanceTransfer` contract handles setting allowances on tokens, giving pe
 
 Before integrating contracts can request users’ tokens through `Permit2`, users must approve the `Permit2` contract through the specific token contract. To see a detailed technical reference, visit the Uniswap [documentation site](https://docs.uniswap.org/contracts/permit2/overview).
 
+### Note on viaIR compilation
+Permit2 uses viaIR compilation, so importing and deploying it in an integration for tests will require the integrating repository to also use viaIR compilation. This is often quite slow, so can be avoided using the precompiled `DeployPermit2` utility:
+```
+import {DeployPermit2} from "permit2/test/utils/DeployPermit2.sol";
+
+contract MyTest is DeployPermit2 {
+    address permit2;
+
+    function setUp() public {
+        permit2 = deployPermit2();
+    }
+}
+```
+
 ## Bug Bounty
 
 This repository is subject to the Uniswap Labs Bug Bounty program, per the terms defined [here](https://uniswap.org/bug-bounty).