Python: inline init_module_submodule_defn into ImportResolution

The new-dataflow ImportResolution module only used
semmle.python.essa.SsaDefinitions for the 5-line helper predicate
SsaSource::init_module_submodule_defn. Inline it locally and drop the
dependency on legacy SsaDefinitions. This is the only remaining direct
import of semmle.python.essa.* in the new dataflow stack, so dropping
it makes the layering cleaner.

Semantic noop on the current SSA: SsaSourceVariable.getName() and
GlobalVariable.getId() both project the same DB column
(variable(_,_,result)), and the old call's 'init.getEntryNode() = f'
join was just constraining init = package via Scope.getEntryNode()'s
functional uniqueness. RA dump of accesses.ql confirms only the
expected predicate-rename shuffle; all 70 dataflow + ApiGraphs library
tests pass.

This factors out commit 8cab5a20f2 from the larger shared-CFG
migration #21925.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/ql/lib/semmle/python/dataflow/new/internal/ImportResolution.qll

@@ -9,7 +9,19 @@ private import semmle.python.dataflow.new.DataFlow
 private import semmle.python.dataflow.new.internal.ImportStar
 private import semmle.python.dataflow.new.TypeTracking
 private import semmle.python.dataflow.new.internal.DataFlowPrivate
-private import semmle.python.essa.SsaDefinitions
+
+/**
+ * Holds if `init` is a package's `__init__.py` and `var` is a global variable in
+ * `init` whose name matches a submodule of the package.
+ *
+ * Inlined from `SsaSource::init_module_submodule_defn` to avoid pulling
+ * `semmle.python.essa.SsaDefinitions` into the new dataflow stack.
+ */
+private predicate initModuleSubmoduleDefn(GlobalVariable var, Module init) {
+  init.isPackageInit() and
+  exists(init.getPackage().getSubModule(var.getId())) and
+  var.getScope() = init
+}
 
 /**
  * Python modules and the way imports are resolved are... complicated. Here's a crash course in how
@@ -326,7 +338,7 @@ module ImportResolution {
     // imported yet.
     exists(string submodule, Module package, EssaVariable var |
       submodule = var.getName() and
-      SsaSource::init_module_submodule_defn(var.getSourceVariable(), package.getEntryNode()) and
+      initModuleSubmoduleDefn(var.getSourceVariable(), package) and
       m = getModuleFromName(package.getPackageName() + "." + submodule) and
       result.asCfgNode() = var.getDefinition().(EssaNodeDefinition).getDefiningNode()
     )