fix(ir): resolve forward alias in top-level global annotations (issue 0070)

Issue 0069's resolveForwardIdentifierAliases fixpoint runs at the END of
scanDecls, but top-level var_decl globals and typed module constants had
their annotations resolved via resolveType(ta) inside the SAME scan loop,
before the fixpoint. So a forward identifier alias (`A :: B; B :: s32;`)
used as a global's type (`g : A = 7;`) was still absent from
type_alias_map: resolveType fabricated an empty-struct stub, and the global
got a type mismatching its initializer at LLVM verification (the typed-const
path `K : A : 42;` silently mistyped the constant instead).

Split scanDecls into two passes: pass 1 registers function/type/alias facts,
then resolveForwardIdentifierAliases converges the aliases, then pass 2
registers var_decl globals (registerTopLevelGlobal) and typed module
constants (registerTypedModuleConst) against the converged alias map.
Globals/typed-consts can't be named in a type position, so deferring them
past type/alias registration is order-safe; the untyped module-const branch
(no annotation to resolve) stays in pass 1.

One incidental IR snapshot reorder (examples/1309: user globals now emit
after foreign-class globals — semantically identical, program still exits 0).

Regression: examples/0133-types-forward-alias-global.sx (forward-alias global
+ typed const). Gate: zig build, zig build test, run_examples.sh -> 354/0.

examples/expected/0133-types-forward-alias-global.exit

@@ -0,0 +1 @@
+42

examples/expected/0133-types-forward-alias-global.stdout

@@ -0,0 +1,2 @@
+global g: 7
+const K:  35

examples/expected/1309-ffi-objc-class-method-lowering.ir

@@ -1,9 +1,9 @@
 
+@__SxFoo_state_ivar = internal global ptr null
+@__SxFoo_class = internal global ptr null
 @OS = internal global i64 0
 @ARCH = internal global i64 0
 @POINTER_SIZE = internal global i64 8
-@__SxFoo_state_ivar = internal global ptr null
-@__SxFoo_class = internal global ptr null
 @__sx_default_context = internal global { { ptr, ptr, ptr }, ptr } { { ptr, ptr, ptr } { ptr null, ptr @__thunk_CAllocator_Allocator_alloc, ptr @__thunk_CAllocator_Allocator_dealloc }, ptr null }
 @__sx_objc_cstr_dealloc = internal global [8 x i8] c"dealloc\00"
 @str = private unnamed_addr constant [2 x i8] c"0\00", align 1