Zcu: fix nav_ty dependency on nav_val

In the case where a declaration has no type annotation, the interaction
between resolution of `nav_ty` and `nav_val` is a little fiddly because
of the fact that resolving `nav_val` actually implicitly resolves the
type as well. This means `nav_ty` never gets an opporunity to mark its
dependency on the `nav_val`. So, `ensureNavValUpToDate` needs to be the
one to do it. It can't do it too early, though; otherwise, our marking
of dependees as out-of-date/up-to-date will go wrong.

Resolves: #23959

test/incremental/dependency_on_type_of_inferred_global

@@ -0,0 +1,30 @@
+#target=x86_64-linux-selfhosted
+#target=x86_64-linux-cbe
+#target=x86_64-windows-cbe
+#target=wasm32-wasi-selfhosted
+#update=initial version
+#file=main.zig
+const foo = @as(u8, 123);
+comptime {
+    // depends on value of `foo`
+    if (foo != 123) unreachable;
+}
+comptime {
+    // depends on type of `foo`
+    if (@TypeOf(&foo) != *const u8) unreachable;
+}
+pub fn main() void {}
+#expect_stdout=""
+#update=change the type
+#file=main.zig
+const foo = @as(u16, 123);
+comptime {
+    // depends on value of `foo`
+    if (foo != 123) unreachable;
+}
+comptime {
+    // depends on type of `foo`
+    if (@TypeOf(&foo) != *const u8) unreachable;
+}
+pub fn main() void {}
+#expect_error=main.zig:8:37: error: reached unreachable code