[ink_e2e] move building of contracts from macro codegen to runtime

[ascjones]

Originally the contracts needed to be build during codegen in order that the resulting metadata could be used to generate the API for invoking the contract. However since the change to use the contract as a depencency in #1518, it is no longer required to do this at the macro expansion test.

I believe it would be much cleaner and clearer to build the contracts at the runtime stage.

As part of this we can refactor how the contracts are built, for example we may no longer need to have the global static ALREADY_BUILT_CONTRACTS, and instead rely on the cargo file locking to prevent races. Now that cargo contract build returns also immediately if there are no changes in the contract I believe this may be sufficient, although it needs testing.

Extraced from #1830