feat(ISwapExecutor): Add ISwapExecutor and docs

evm/src/interfaces/ISwapExecutor.sol

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.7.5;
+
+import "openzeppelin-contracts/contracts/interfaces/IERC20.sol";
+
+pragma abicoder v2;
+
+interface ISwapExecutor {
+    /**
+     * @notice Performs a swap on a liquidity pool.
+     * @dev This method can either take the amount of the input token or the
+     * amount
+     * of the output token that we would like to swap. If called with the amount
+     * of
+     * the  input token, the amount of the output token will be returned, and
+     * vice
+     * versa. Whether it is the input or output that is given, is encoded in the
+     * data
+     * parameter.
+     *
+     * Note Part of the informal interface is that the executor supports sending
+     * the received
+     *  tokens to a receiver address. If the underlying smart contract does not
+     * provide this
+     *  functionality consider adding an additional transfer in the
+     * implementation.
+     *
+     *  This function is marked as `payable` to accommodate delegatecalls, which
+     * can forward
+     *  a potential `msg.value` to it.
+     *
+     * @param givenAmount The amount of either the input token or output token
+     * to swap.
+     * @param data Data that holds information necessary to perform the swap.
+     * @return calculatedAmount The amount of either the input token or output
+     * token
+     * swapped, depending on the givenAmount inputted.
+     */
+    function swap(uint256 givenAmount, bytes calldata data)
+        external
+        payable
+        returns (uint256 calculatedAmount);
+}
+
+interface ISwapExecutorErrors {
+    error InvalidParameterLength(uint256);
+    error UnknownPoolType(uint8);
+}