Add natvis visualizers for json_document and json_view

nlohmann_json.natvis had no entries for the view and document types, so a
debugger showed the raw node index. Add visualizers for
basic_json_document<*,*>, basic_json_view<*,*> and detail::view::node.

A document is a flat index into the source text, so the strings of the
direct children can be read through document_data::base, while the
children of nested containers are shown as nodes (kind, size, numbers;
strings only by length). Containers with edits (node_flags::moved) are
not expanded. The types live in the same inline namespaces as basic_json
and view_mode is covered by a wildcard, so the ABI tags do not multiply
with it; the file grows from 862 KB to 1.7 MB.

Also correct the ABI tag count (11) in the --all size note.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tools/generate_natvis/generate_natvis.py

@@ -95,7 +95,7 @@ if __name__ == '__main__':
                                 'optional) of one configuration to add to the default namespaces; can be repeated')
     selection.add_argument('--all', action='store_true',
                            help='Generate the namespaces for every combination of ABI tags; the file size doubles '
-                                'with each ABI tag (about 60 MB for 12 tags)')
+                                'with each ABI tag (about 60 MB for 11 tags)')
     parser.add_argument('--list-tags', action='store_true',
                         help='List the ABI tags with the macros that enable them, and exit')
     parser.add_argument('--output', metavar='FILE',