gh-136640: Correct the description of AST location attributes

Eight of the types generated from ``Parser/Python.asdl`` carry the
``lineno``/``col_offset``/``end_lineno``/``end_col_offset`` attributes --
``stmt``, ``expr``, ``excepthandler``, ``arg``, ``keyword``, ``alias``,
``pattern`` and ``type_param`` -- but the documentation named only
``ast.expr`` and ``ast.stmt``.

The same block also stated that the end positions are always optional.
That holds for the six types that declare them as ``int?`` in the
grammar; ``pattern`` and ``type_param`` declare them as ``int``, and
compiling a tree whose ``pattern`` or ``type_param`` node is missing
``end_lineno`` raises ``TypeError``.

The first paragraph follows the wording approved in GH-136868 and the
two review suggestions on it, except that it keeps the original
"Instances of": the classes themselves expose nothing, so
``hasattr(ast.Name, 'lineno')`` is false.  The cross-reference uses
``:ref:``, matching the rest of the file.

Author: v0ropaev

Doc/library/ast.rst

@@ -90,17 +90,21 @@ Node classes
                   end_lineno
                   end_col_offset
 
-      Instances of :class:`ast.expr` and :class:`ast.stmt` subclasses have
+      Instances of most classes in the :mod:`!ast` module have the
       :attr:`lineno`, :attr:`col_offset`, :attr:`end_lineno`, and
-      :attr:`end_col_offset` attributes.  The :attr:`lineno` and :attr:`end_lineno`
+      :attr:`end_col_offset` attributes, including all subclasses of
+      :class:`ast.expr`, :class:`ast.stmt` and others (see the abstract grammar
+      :ref:`above <abstract-grammar>`).  The :attr:`lineno` and :attr:`end_lineno`
       are the first and last line numbers of source text span (1-indexed so the
       first line is line 1) and the :attr:`col_offset` and :attr:`end_col_offset`
       are the corresponding UTF-8 byte offsets of the first and last tokens that
       generated the node. The UTF-8 offset is recorded because the parser uses
       UTF-8 internally.
 
       Note that the end positions are not required by the compiler and are
-      therefore optional. The end offset is *after* the last symbol, for example
+      therefore optional, except for :class:`ast.pattern` and
+      :class:`ast.type_param` nodes, for which the compiler requires them.
+      The end offset is *after* the last symbol, for example
       one can get the source segment of a one-line expression node using
       ``source_line[node.col_offset : node.end_col_offset]``.