Add support for PancakeSwapV3

[gnarlycow]

This change adds two libraries PoolAddressPancakeSwapV3 and CallbackValidationPancakeSwapV3 that support PCSV3; all existing contract code remains unchanged except for moving the PoolKey struct definition to a separate PoolKey.sol file.

Tests have been refactored to test against both UniV3 and PCSV3 implementations where applicable.

Notable differences between UniV3 and PCSV3:

• PCSV3 uses the deployer contract address instead of the factory when computing pool addresses. The two added libraries reflect this difference.
• PCSV3 pool slot0's feeProtocol is uint32 instead of uint8. A PCSV3 counterpart of the PoolCaller library has NOT been created because Aperture doesn't have an immediate need for this. However, all other functions in the PoolCaller library should also work for PCSV3.
• PCSV3 pool's swap callback is named pancakeV3SwapCallback instead of uniswapV3SwapCallback. This is reflected in the PoolCaller swap test (PoolCaller.t.sol).