fix parsing of generator in argument list to actually match Python grammaer (PY-6926)

python/testData/psi/GeneratorList.py

@@ -0,0 +1 @@
+list(int(i) for i in '1', '2')

python/testData/psi/GeneratorList.txt

@@ -0,0 +1,31 @@
+PyFile:GeneratorList.py
+  PyExpressionStatement
+    PyCallExpression: list
+      PyReferenceExpression: list
+        PsiElement(Py:IDENTIFIER)('list')
+      PyArgumentList
+        PsiElement(Py:LPAR)('(')
+        PyGeneratorExpression
+          PyCallExpression: int
+            PyReferenceExpression: int
+              PsiElement(Py:IDENTIFIER)('int')
+            PyArgumentList
+              PsiElement(Py:LPAR)('(')
+              PyReferenceExpression: i
+                PsiElement(Py:IDENTIFIER)('i')
+              PsiElement(Py:RPAR)(')')
+          PsiWhiteSpace(' ')
+          PsiElement(Py:FOR_KEYWORD)('for')
+          PsiWhiteSpace(' ')
+          PyTargetExpression: i
+            PsiElement(Py:IDENTIFIER)('i')
+          PsiWhiteSpace(' ')
+          PsiElement(Py:IN_KEYWORD)('in')
+          PsiWhiteSpace(' ')
+          PyStringLiteralExpression: 1
+            PsiElement(Py:SINGLE_QUOTED_STRING)(''1'')
+        PsiElement(Py:COMMA)(',')
+        PsiWhiteSpace(' ')
+        PyStringLiteralExpression: 2
+          PsiElement(Py:SINGLE_QUOTED_STRING)(''2'')
+        PsiElement(Py:RPAR)(')')