Ensure needed imports from typing are included in type-stubs

Leverages the `writeSection` machinery, with a tweak to specify to add a
new section to the beginning of a file, after the header. This ensures
the required imports gets updated (and also only imported once per file)
if new imports are needed for type-hints. Hint: there's a few more to come.

etgtools/pi_generator.py

@@ -77,6 +77,12 @@ header_pyi = """\
 
 """
 
+typing_imports = """\
+from __future__ import annotations
+from typing import Any
+
+"""
+
 #---------------------------------------------------------------------------
 
 def piIgnored(obj):
@@ -112,18 +118,21 @@ class PiWrapperGenerator(generators.WrapperGeneratorBase, FixWxPrefix):
 
         if not SKIP_PI_FILE:
             _checkAndWriteHeader(destFile_pi, header_pi, module.docstring)
+            self.writeSection(destFile_pi, 'typing-imports', typing_imports, at_end=False)
             self.writeSection(destFile_pi, module.name, stream.getvalue())
 
         if not SKIP_PYI_FILE:
             _checkAndWriteHeader(destFile_pyi, header_pyi, module.docstring)
+            self.writeSection(destFile_pyi, 'typing-imports', typing_imports, at_end=False)
             self.writeSection(destFile_pyi, module.name, stream.getvalue())
 
 
-    def writeSection(self, destFile, sectionName, sectionText):
+    def writeSection(self, destFile, sectionName, sectionText, at_end = True):
         """
         Read all the lines from destFile, remove those currently between
         begin/end markers for sectionName (if any), and write the lines back
         to the file with the new text in sectionText.
+        `at_end` determines where in the file the section is added when missing
         """
         sectionBeginLine = -1
         sectionEndLine = -1
@@ -139,10 +148,23 @@ class PiWrapperGenerator(generators.WrapperGeneratorBase, FixWxPrefix):
                 sectionEndLine = idx
 
         if sectionBeginLine == -1:
-            # not there already, add to the end
-            lines.append(sectionBeginMarker + '\n')
-            lines.append(sectionText)
-            lines.append(sectionEndMarker + '\n')
+            if at_end:
+                # not there already, add to the end
+                lines.append(sectionBeginMarker + '\n')
+                lines.append(sectionText)
+                lines.append(sectionEndMarker + '\n')
+            else:
+                # not there already, add to the beginning
+                # Skip the header
+                idx = 0
+                for idx, line in enumerate(lines):
+                    if not line.startswith('#'):
+                        break
+                lines[idx+1:idx+1] = [
+                    sectionBeginMarker + '\n',
+                    sectionText,
+                    sectionEndMarker + '\n',
+                ]
         else:
             # replace the existing lines
             lines[sectionBeginLine+1:sectionEndLine] = [sectionText]