Fix type annotations in pandas.core.resample
Part of #25882
- [X] tests passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

This PR addresses the following mypy errors in **pandas.core.resample**:
```
pandas/core/resample.py:34: error: Need type annotation for '_shared_docs_kwargs'
pandas/core/resample.py:876: error: All conditional function variants must have identical signatures
pandas/core/resample.py:884: error: All conditional function variants must have identical signatures
pandas/core/resample.py:891: error: All conditional function variants must have identical signatures
pandas/core/resample.py:1101: error: Definition of "_upsample" in base class "_GroupByMixin" is incompatible with definition in base class "DatetimeIndexResampler"
pandas/core/resample.py:1101: error: Definition of "_upsample" in base class "_GroupByMixin" is incompatible with definition in base class "Resampler"
pandas/core/resample.py:1101: error: Definition of "_downsample" in base class "_GroupByMixin" is incompatible with definition in base class "DatetimeIndexResampler"
pandas/core/resample.py:1101: error: Definition of "_groupby_and_aggregate" in base class "_GroupByMixin" is incompatible with definition in base class "Resampler"
pandas/core/resample.py:1217: error: Definition of "_upsample" in base class "_GroupByMixin" is incompatible with definition in base class "PeriodIndexResampler"
pandas/core/resample.py:1217: error: Definition of "_upsample" in base class "_GroupByMixin" is incompatible with definition in base class "DatetimeIndexResampler"
pandas/core/resample.py:1217: error: Definition of "_upsample" in base class "_GroupByMixin" is incompatible with definition in base class "Resampler"
pandas/core/resample.py:1217: error: Definition of "_downsample" in base class "_GroupByMixin" is incompatible with definition in base class "PeriodIndexResampler"
pandas/core/resample.py:1217: error: Definition of "_downsample" in base class "_GroupByMixin" is incompatible with definition in base class "DatetimeIndexResampler"
pandas/core/resample.py:1217: error: Definition of "_groupby_and_aggregate" in base class "_GroupByMixin" is incompatible with definition in base class "Resampler"
pandas/core/resample.py:1247: error: Definition of "_upsample" in base class "_GroupByMixin" is incompatible with definition in base class "DatetimeIndexResampler"
pandas/core/resample.py:1247: error: Definition of "_upsample" in base class "_GroupByMixin" is incompatible with definition in base class "Resampler"
pandas/core/resample.py:1247: error: Definition of "_downsample" in base class "_GroupByMixin" is incompatible with definition in base class "DatetimeIndexResampler"
pandas/core/resample.py:1247: error: Definition of "_groupby_and_aggregate" in base class "_GroupByMixin" is incompatible with definition in base class "Resampler"
pandas/core/resample.py:1299: error: Incompatible types in assignment (expression has type "Tuple[str, ...]", base class "Grouper" defined the type as "Tuple[str, str, str, str, str]")
```