[3.9] bpo-40204: Allow pre-Sphinx 3 syntax in the doc (GH-21844) (GH-21901)

* bpo-40204: Allow pre-Sphinx 3 syntax in the doc (GH-21844)

Enable Sphinx 3.2 "c_allow_pre_v3" option and disable the
c_warn_on_allowed_pre_v3 option to make the documentation compatible
with Sphinx 2 and Sphinx 3.

(cherry picked from commit 423e77d6de497931585d1883805a9e3fa4096b0b)

* bpo-40204: Fix Sphinx sytanx in howto/instrumentation.rst (GH-21858)

Use generic '.. object::' to declare markers, rather than abusing
'..  c:function::' which fails on Sphinx 3.

(cherry picked from commit 43577c01a2ab49122db696e9eaec6cb31d11cc81)

* bpo-40204: Fix duplicates in the documentation (GH-21857)

Fix two Sphinx 3 issues:

Doc/c-api/buffer.rst:304: WARNING: Duplicate C declaration, also defined in 'c-api/buffer'.
Declaration is 'PyBUF_ND'.

Doc/c-api/unicode.rst:1603: WARNING: Duplicate C declaration, also defined in 'c-api/unicode'.
Declaration is 'PyObject* PyUnicode_Translate(PyObject *str, PyObject *table, const char *errors)'.

(cherry picked from commit 46d10b1237c67ff8347f533eda6a5468d098f7eb)

* bpo-40204: Add :noindex: in the documentation (GH-21859)

Add :noindex: to duplicated documentation to fix "duplicate object
description" errors.

For example, fix this Sphinx 3 issue:

Doc/library/configparser.rst:1146: WARNING: duplicate object
description of configparser.ConfigParser.optionxform, other instance
in library/configparser, use :noindex: for one of them

(cherry picked from commit d3ded080482beae578faa704b13534a62d066f9f)

* bpo-40204, doc: Fix syntax of C variables (GH-21846)

For example, fix the following Sphinx 3 errors:

Doc/c-api/buffer.rst:102: WARNING: Error in declarator or parameters
Invalid C declaration: Expected identifier in nested name. [error at 5]
  void \*obj
  -----^

Doc/c-api/arg.rst:130: WARNING: Unparseable C cross-reference: 'PyObject*'
Invalid C declaration: Expected end of definition. [error at 8]
  PyObject*
  --------^

The modified documentation is compatible with Sphinx 2 and Sphinx 3.

(cherry picked from commit 474652fe9346382dbf793f20b671eb74668bebde)

* bpo-40204: Fix reference to terms in the doc (GH-21865)

Sphinx 3 requires to refer to terms with the exact case.

For example, fix the Sphinx 3 warning:

Doc/library/pkgutil.rst:71: WARNING: term Loader not found in case
sensitive match.made a reference to loader instead.

(cherry picked from commit bb0b08540cc93e56f3f1bde1b39ce086d9e35fe1)

* bpo-40204: Fix duplicated productionlist names in the doc (GH-21900)

Sphinx 3 disallows having more than one productionlist markup with
the same name. Simply remove names in this case, since names are not
shown anyway. For example, fix the Sphinx 3 warning:

Doc/reference/introduction.rst:96: duplicate token description
of *:name, other instance in reference/expressions

(cherry picked from commit 1abeda80f760134b4233608e2c288790f955b95a)
diff --git a/Doc/c-api/unicode.rst b/Doc/c-api/unicode.rst
index 4750f24..8a312ae 100644
--- a/Doc/c-api/unicode.rst
+++ b/Doc/c-api/unicode.rst
@@ -199,7 +199,7 @@
    .. versionadded:: 3.3
 
 
-.. c:function:: PyUnicode_MAX_CHAR_VALUE(PyObject *o)
+.. c:macro:: PyUnicode_MAX_CHAR_VALUE(o)
 
    Return the maximum code point that is suitable for creating another string
    based on *o*, which must be in the "canonical" representation.  This is
@@ -1503,17 +1503,21 @@
 
 The following codec API is special in that maps Unicode to Unicode.
 
-.. c:function:: PyObject* PyUnicode_Translate(PyObject *unicode, \
-                              PyObject *mapping, const char *errors)
+.. c:function:: PyObject* PyUnicode_Translate(PyObject *str, PyObject *table, const char *errors)
 
-   Translate a Unicode object using the given *mapping* object and return the
-   resulting Unicode object.  Return ``NULL`` if an exception was raised by the
+   Translate a string by applying a character mapping table to it and return the
+   resulting Unicode object. Return ``NULL`` if an exception was raised by the
    codec.
 
-   The *mapping* object must map Unicode ordinal integers to Unicode strings,
-   integers (which are then interpreted as Unicode ordinals) or ``None``
-   (causing deletion of the character).  Unmapped character ordinals (ones
-   which cause a :exc:`LookupError`) are left untouched and are copied as-is.
+   The mapping table must map Unicode ordinal integers to Unicode ordinal integers
+   or ``None`` (causing deletion of the character).
+
+   Mapping tables need only provide the :meth:`__getitem__` interface; dictionaries
+   and sequences work well.  Unmapped character ordinals (ones which cause a
+   :exc:`LookupError`) are left untouched and are copied as-is.
+
+   *errors* has the usual meaning for codecs. It may be ``NULL`` which indicates to
+   use the default error handling.
 
 
 .. c:function:: PyObject* PyUnicode_TranslateCharmap(const Py_UNICODE *s, Py_ssize_t size, \
@@ -1616,23 +1620,6 @@
    characters are not included in the resulting strings.
 
 
-.. c:function:: PyObject* PyUnicode_Translate(PyObject *str, PyObject *table, \
-                              const char *errors)
-
-   Translate a string by applying a character mapping table to it and return the
-   resulting Unicode object.
-
-   The mapping table must map Unicode ordinal integers to Unicode ordinal integers
-   or ``None`` (causing deletion of the character).
-
-   Mapping tables need only provide the :meth:`__getitem__` interface; dictionaries
-   and sequences work well.  Unmapped character ordinals (ones which cause a
-   :exc:`LookupError`) are left untouched and are copied as-is.
-
-   *errors* has the usual meaning for codecs. It may be ``NULL`` which indicates to
-   use the default error handling.
-
-
 .. c:function:: PyObject* PyUnicode_Join(PyObject *separator, PyObject *seq)
 
    Join a sequence of strings using the given *separator* and return the resulting