Add getattr overload variants to help mypy type inference

[JukkaL]

These silence errors about missing type annotations for calls
like these:

x = getattr(o, 'a', [])
y = getattr(o, 'b', {})

This is basically a generalization of #5518 and other overloads we already
have.

This works around python/mypy#11572. I encountered the issue in several
places when testing recent typeshed against an internal repo.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

paasta (https://github.com/yelp/paasta.git)
- paasta_tools/kubernetes_tools.py:2106: error: Need type annotation for "stream_lines"

sphinx (https://github.com/sphinx-doc/sphinx.git)
- sphinx/util/requests.py: note: In function "is_ssl_error":
- sphinx/util/requests.py:54:16: error: Need type annotation for "args"
- sphinx/ext/napoleon/docstring.py: note: In member "_lookup_annotation" of class "GoogleDocstring":
- sphinx/ext/napoleon/docstring.py:864:31: error: Need type annotation for "localns"
- sphinx/ext/viewcode.py: note: In function "env_purge_doc":
- sphinx/ext/viewcode.py:161:15: error: Need type annotation for "modules"

flake8 (https://github.com/pycqa/flake8.git)
- src/flake8/plugins/manager.py:508: error: Need type annotation for "plugins"
- src/flake8/plugins/manager.py:517: error: Need type annotation for "plugins"
- src/flake8/plugins/manager.py:526: error: Need type annotation for "plugins"

pandas (https://github.com/pandas-dev/pandas.git)
- pandas/io/stata.py:2598: error: Need type annotation for "convert_strl"  [var-annotated]

pylint (https://github.com/pycqa/pylint.git)
- pylint/pyreverse/inspector.py:184: error: Need type annotation for "specializations"  [var-annotated]
- pylint/checkers/variables.py:1781: error: Need type annotation for "elements"  [var-annotated]
- pylint/checkers/typecheck.py:1378: error: Need type annotation for "already_filled_keywords"  [var-annotated]

freqtrade (https://github.com/freqtrade/freqtrade.git)
- freqtrade/strategy/informative_decorator.py:56: error: Need type annotation for "informative_pairs"

pytest (https://github.com/pytest-dev/pytest.git)
- src/_pytest/mark/structures.py:365: error: Need type annotation for "mark_list"  [var-annotated]
- src/_pytest/fixtures.py:1323: note: (Skipping most remaining errors due to unresolved imports or missing stubs; fix these first)
+ src/_pytest/fixtures.py:1323: error: Unexpected keyword argument "params" for "FixtureFunctionMarker"  [call-arg]

werkzeug (https://github.com/pallets/werkzeug.git)
- src/werkzeug/local.py:123: error: Need type annotation for "rv"
+ tests/test_wrappers.py:833: note: Use "-> None" if function does not return a value
- tests/test_wrappers.py:833: note: (Skipping most remaining errors due to unresolved imports or missing stubs; fix these first)
+ tests/test_wrappers.py:856: note: (Skipping most remaining errors due to unresolved imports or missing stubs; fix these first)

edgedb (https://github.com/edgedb/edgedb.git)
- edb/common/parametric.py:150:36: error: Need type annotation for "base_non_type_params"
- edb/edgeql/declarative.py:919:23: error: Need type annotation for "ast_subcommands"
- edb/pgsql/compiler/relctx.py:94:28: error: Need type annotation for "view_path_id_map"
- edb/server/connpool/pool.py:526:16: error: No overload variant of "get" of "Mapping" matches argument type "str"
- edb/server/connpool/pool.py:526:16: note: Possible overload variant:
- edb/server/connpool/pool.py:526:16: note:     def get(self, key: <nothing>) -> None
- edb/server/connpool/pool.py:526:16: note:     <1 more non-matching overload not shown>

pyppeteer (https://github.com/pyppeteer/pyppeteer.git)
- pyppeteer/network_manager.py:157: error: No overload variant of "get" of "Mapping" matches argument type "str"
- pyppeteer/network_manager.py:157: note: Possible overload variant:
- pyppeteer/network_manager.py:157: note:     def get(self, key: <nothing>) -> None
- pyppeteer/network_manager.py:157: note:     <1 more non-matching overload not shown>
- pyppeteer/network_manager.py:158: error: No overload variant of "get" of "Mapping" matches argument type "str"
- pyppeteer/network_manager.py:158: note: Possible overload variant:
- pyppeteer/network_manager.py:158: note:     def get(self, key: <nothing>) -> None
- pyppeteer/network_manager.py:158: note:     <1 more non-matching overload not shown>