[NS 1] Add sub-module mounts support + codegen

[aasoni]

Description of Changes

Add a new recursive "mounts" field to add submodules to module def. Handle code generation for each language.
Handle identifiers with "/" or "." in the name to handle namespaced reducers (e.g. lib/reducer) and namespaced tables (lib.table).

Handle code generation for the recursive type. This needed some special handling in code generation for typescript and c++.
Typescript codegen in particular is quite complex as it tries to handle circular dependency generically. C++ on the other hand is a lot simpler because it hard-codes a special handling of the V10 definition but doesn't solve circular dependencies in general.
I would advice against solving circular dependencies in a generic way for C++ however we could consider modifying the typescript code gen to just have special handling for the V10 recursive definition which would simplify the code quite a lot. I went down the rabbit hole of handling this generically and came out on the other side, but if there is strong opinion to keep the codegen code simple, I am happy to revisit and align to the C++ way.

API and ABI breaking changes

The change is purely additive and newer host versions will accept older module defs. However older host versions will not accept new module defs.

Expected complexity level and risk

5 - While this specific PR is maybe a 4, the overall namespace change is definitely 5. This is a pretty significant change. It's a large diff which touches the module def and changes code that hasn't been touched in a long time (e.g. Identifier).

Testing

Beyond the rust tests defined in this PR, the following tests were done on the full PR sequence once the entire namespace feature was implemented for typescript:
Feature Test Checklist

Module:

• root module can import another module and mount it with a namespace under its schema
• root module and submodule can have the same function and table names without conflicting
• ctx.db.lib.lib_table is readable/writable inside root module reducer
• ctx.db.lib.lib_table is readable/writable inside root module procedure withTx block
• library_reducer(ctx.as.lib) is callable inside root module reducer

Client

• Client can subscribe to lib.library_table
• Client can subscribe to lib.library_view
• Client can call lib/library_reducer
• Client can call lib/library_procedure
• Client can subscribe to lib.sublib.sublib_table
• Client can subscribe to lib.sublib.sublib_view
• Client can call lib/sublib/sublib_reducer
• Client can call lib/sublib/sublib_procedure

CLI

• CLI can subscribe to lib.library_table
• CLI can subscribe to lib.library_view
• CLI can call lib/library_reducer
• CLI can call lib/library_procedure
• CLI can subscribe to lib.sublib.sublib_table
• CLI can subscribe to lib.sublib.sublib_view
• CLI can call lib/sublib/sublib_reducer
• CLI can call lib/sublib/sublib_procedure

Migration

• Module migrates without issue from having a submodule to not having a submodule
• Module migrates without issue from not having a submodule to having a submodule
• Module migrates without issue when having a submodule and root module change occurs (change reducer signature, add table, add column with default, change reducer function body, change index)
• Module migrates without issue when having a submodule and a submodule change occurs (change reducer signature, add table, add column with default, change reducer function body, change index)

Commit Log

• Module loads fine from commit log
• Module snapshot is created without issue
• Module loads fine from snapshot

[gefjon]

I'm really unhappy with the codegen changes in both TypeScript and C++ here. The TypeScript changes seem very complicated and finnickey, and the C++ changes are an obviously brittle special case. I don't understand why we don't just move to generating a single file for the whole module, if generating individual files and importing across them is causing so many problems.

[JasonAtClockwork]

The C++ side is working, I've also come up with two options to make it cleaner when we fully integrate the C++ sub-modules.

[aasoni]

check if this is still necessary

[aasoni]

Change to option

[aasoni]

Move this to crates/codegen/examples/regen-typescript-moduledef.rs

[aasoni]

Use the new validation function

[aasoni]

Rename mounts -> submodules everywhere

[cloutiertyler]

Alessandro and I went over this in person. I think this looks good. There's a few nits we talked about.

I would also like to add any new syntax we have to module-test-ts.