Add new precompile PrecompileRegistry

[nanocryk]

What does it do?

Implements this proposal: https://forum.moonbeam.foundation/t/proposal-status-idea-precompile-to-check-active-precompiles/384

It also allows for any user to set the "dummy code" of precompiles to make them callable from Solidity (which adds an empty code check). This is currently done through democracy with set_storage, which is far from ideal.

For audit

Ensure that it is not possible to change the code of non-precompile addresses.

[notlesh]

Looks good, I think... I am unclear about a couple things:

• Anyone can insert the dummy code as long as the precompile is active? I thought we sometimes used this bug feature to control whether a contract could call a precompile, allowing cases where only an EOA can call.
• There is no removing the dummy code, but a precompile could be modified (via runtime upgrade) to become inactive, which would cause it to always revert when called -- right?

[nanocryk]

Anyone can insert the dummy code as long as the precompile is active? I thought we sometimes used this bug feature to control whether a contract could call a precompile, allowing cases where only an EOA can call.

This only prevents code written in Solidity that uses interfaces, which automatically appends codesize checks. address(X).call(...) or assembly will not perform the size-check. This is why we have proper capabilities list with PrecompileSetBuilder.

There is no removing the dummy code, but a precompile could be modified (via runtime upgrade) to become inactive, which would cause it to always revert when called -- right?

Precompile should be replaced with RemovedPrecompileAt, but otherwise yes if it is really removed from the precompile set it will use the "always revert" code.