Yul: Immutable AST class with top-level block

[clonker]

• depends on PR Yul: Add const version of FunctionCallFinder #15253

[ekpyron]

Looks like this is in dire need of a rebase

[cameel]

No issues on terms of correctness, but could use better naming and the override in compilability checker could be done differently. See comments.

[cameel]

Unfortunately I did find some new stuff on this second pass:

• I think we should move AsmAnalysisInfo to the AST struct and make it immutable as well. It would reduce the risk of forgetting to update it and we would also be able to calculate it just once per AST.
• YulOptimizerTest allows arbitrary object nesting but does not handle that properly (only cares about the top-level one). And now with the extra copying added by this PR that gets extra unsafe, because we're not doing full copies of the objects. We should safeguard that with some asserts and maybe consider also actually fixing it properly (later, in a separate PR).