Use tk_scaling() instead of a raw Tcl call in IDLE and tkinter tests (#152788)

Replace `tk.call('tk', 'scaling')` with `tk_scaling()`, which
returns a float, in idlelib.util and test_tkinter.widget_tests.

Co-authored-by: serhiy-storchaka

Author: terryjreedy

Lib/idlelib/util.py

@@ -24,7 +24,7 @@
 def fix_scaling(root):  # Called in filelist _test, pyshell, and run.
     """Scale fonts on HiDPI displays, once per process."""
     import tkinter.font
-    scaling = float(root.tk.call('tk', 'scaling'))
+    scaling = root.tk_scaling()
     if scaling > 1.4:
         for name in tkinter.font.names(root):
             font = tkinter.font.Font(root=root, name=name, exists=True)

Lib/test/test_tkinter/widget_tests.py

@@ -34,7 +34,7 @@ def scaling(self):
         try:
             return self._scaling
         except AttributeError:
-            self._scaling = float(self.root.call('tk', 'scaling'))
+            self._scaling = self.root.tk_scaling()
             return self._scaling
 
     def _str(self, value):