[WIP] Update to solidity 0.8.12

[ChrisiPK]

As requested in #271, this is an update of all the smart contracts to Solidity 0.8.12

Open issues:

• [ ] Replacement for @uniswap/lib: currently using third-party fork which is compatible with 0.8
• [ ] Depend on 0.8 compatible version of @uniswap/v3-core: currently using the GitHub branch directly as no version is released yet
• [ ] Compilation fails with Stack too deep when compiling inline assembly: Variable pos is 19 slot(s) too deep inside the stack.

Any feedback on the current progress and how to approach the issues would be very much appreciated!

[stale[bot]]

Is this still relevant? If so, what is blocking it? Is there anything you can do to help move it forward?

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.