Support Solidity versions up to 0.8.22

[Xanewok]

The new versions are 0.8.20, 0.8.21 and 0.8.22.

In terms of the language itself:

https://soliditylang.org/blog/2023/05/10/solidity-0.8.20-release-announcement

• N/A

https://soliditylang.org/blog/2023/07/19/solidity-0.8.21-release-announcement/

• Allow qualified access to events from other contracts.
• Relax restrictions on initialization of immutable variables. Reads and writes may now happen at any point at construction time outside of functions and modifiers. Explicit initialization is no longer mandatory.

https://soliditylang.org/blog/2023/10/25/solidity-0.8.22-release-announcement

• Allow defining events at file level - support Solidity v0.8.22 syntax #648

[OmarTawfik]

passing to @AntonyBlakey for the remaining items (possible changes to binding).

[AntonyBlakey]

This issue is about updating our spec, but as far as binding is concerned, there is nothing to update because binding doesn't exist, so it's only applicable to syntax, which is done.