An imported module's top-level statements run from a global constructor (#447)

[ASDAlexander77]

A module with a top-level statement (print("module init") beside its exports) failed to compile when another module imported it as source, under every memory model:

Global is referenced by parentless instruction!
ptr @puts

The importer reads such a module in one of two ways:

• as declarations: its own object file holds the bodies;
• with its bodies: under the JIT without its cache.

Either way, processStatements generated the module's code statements at the importer's module level, outside any function.

The fix has two parts:

• The importer: an imported module's code statements are no longer generated at the importer's level (the new skipCode flag on processStatements). Read as declarations, they belong to the module's own object. Included with its bodies, they run from a global constructor of their own (generateModuleInitCode), after the module's variables are initialized.
• The imported module's own compile: a root that is not the program's entry point runs its top level from a global constructor too. That covers no --entry-point under --emit=obj, a module the JIT cache compiles for an import, and a DLL. Previously generateGlobalEntryCode gave such a root its own main, which was a second main once linked beside the program. The JIT cache already compiled imported modules expecting exactly this ("its top level run from its global constructors").

New tests import-source/import_toplevel.ts + toplevel_module.ts check that the module's statements run once, before main. They run four ways: compiled, -shared, JIT with -shared, and JIT with its cache. The JIT without its cache (--jit-cache=false, the generateModuleInitCode path) prints module init then done. under gc, rc, none and own.

Gate	Result
Windows full suite (Release)	3830/3830
Linux (WSL) full suite	3815/3815
DefaultLib build + suite, release + debug, compile + JIT	gc 159/159; rc, none 158/159 (weakref_basic is gc-only, as on main)
own corpus (compiled without --entry-point, so through the new path)	no flips, no first-error changes (460/618)

Closes #447

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