Draft: Tree rewriting for module initialization

Context

This is a first MR for #3076 (closed)

We introduce a function initialize ?host_function_registry module_map tree main_module_name.

Here module_map is the map of all Wasm_interpreter.Ast.module_ modules.

The function will take transitive closure of all dependencies (the imported modules) of the module main_module_name and will initialise and add them to the tree.

Note This is still WIP as it is blocked by the "unique module" in wasm encoding.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR