Test for docstring with escape characters (#416)

We test explicitly what happens with special characters which are
represented as literals in docstrings in the intermediate stage.

See [this StackOverflow question] for the background.

[this StackOverflow question]: https://stackoverflow.com/questions/57265111/escape-special-characters-in-restructuredtext-sphinx

test_data/intermediate/expected/documentation/docstring_as_raw_string/expected_symbol_table.txt

@@ -0,0 +1,42 @@
+SymbolTable(
+  our_types=[
+    ConstrainedPrimitive(
+      name='Non_empty_XML_serializable_string',
+      inheritances=[],
+      inheritance_id_set=...,
+      ancestors=[],
+      ancestor_id_set=...,
+      descendant_id_set=...,
+      constrainee='STR',
+      is_implementation_specific=False,
+      invariants=[],
+      invariant_id_set=...,
+      description=DescriptionOfOurType(
+        summary='<paragraph>Represent a string with at least one character.</paragraph>',
+        remarks=[
+          textwrap.dedent("""\
+            <paragraph>The string should also be serializable to XML, which is the background for
+            the following constraint.</paragraph>""")],
+        constraints_by_identifier=[
+          [
+            'AASd-130',
+            textwrap.dedent("""\
+              <field_body><paragraph>An attribute with data type "string" shall consist of these characters only:
+              <literal>^[\\x09\\x0A\\x0D\\x20-\\uD7FF\\uE000-\\uFFFD\\u00010000-\\u0010FFFF]*$</literal>.</paragraph></field_body>""")]],
+        parsed=...),
+      parsed=...)],
+  our_types_topologically_sorted=[
+    'Reference to our type Non_empty_XML_serializable_string'],
+  enumerations=[],
+  constrained_primitives=[
+    'Reference to our type Non_empty_XML_serializable_string'],
+  classes=[],
+  concrete_classes=[],
+  constants=[],
+  constants_by_name=...,
+  verification_functions=[],
+  verification_functions_by_name=...,
+  meta_model=MetaModel(
+    description=None,
+    version='dummy',
+    xml_namespace='https://dummy.com'))

test_data/intermediate/expected/documentation/docstring_as_raw_string/meta_model.py

@@ -0,0 +1,20 @@
+# We test for ``\x09`` and other special characters, and make sure they are represented
+# adequately in the string dump of the symbol table.
+
+
+class Non_empty_XML_serializable_string(str, DBC):
+    r"""
+    Represent a string with at least one character.
+
+    The string should also be serializable to XML, which is the background for
+    the following constraint.
+
+    :constraint AASd-130:
+
+        An attribute with data type "string" shall consist of these characters only:
+        ``^[\x09\x0A\x0D\x20-\uD7FF\uE000-\uFFFD\u00010000-\u0010FFFF]*$``.
+    """
+
+
+__version__ = "dummy"
+__xml_namespace__ = "https://dummy.com"