gdbus-codegen: preserve relative indentation in doc comments

This commit also changes the generators for rst, xml and dockbook
to preserve indentation.

Closes #3032

gio/gdbus-2.0/codegen/codegen_docbook.py

@@ -20,6 +20,7 @@
 # Author: David Zeuthen <davidz@redhat.com>
 
 import re
+import textwrap
 from os import path
 
 from . import utils
@@ -340,12 +341,12 @@ class DocbookCodeGenerator:
         return s
 
     def expand_paras(self, s, expandParamsAndConstants):
-        s = self.expand(s, expandParamsAndConstants).strip()
+        s = textwrap.dedent(self.expand(s, expandParamsAndConstants)).rstrip()
         res = []
         if not s.startswith("<para>"):
             res.append("<para>")
         for line in s.split("\n"):
-            line = line.strip()
+            line = line.rstrip()
             if not line:
                 line = "</para><para>"
             res.append(line)