DOC: Fix formatting errors in pandas.api.extensions.ExtensionArray

[HughKelley]

python scripts/validate_docstrings.py pandas.api.extensions.ExtensionArray.view

python scripts/validate_docstrings.py pandas.api.extensions.ExtensionArray.fillna

python scripts/validate_docstrings.py pandas.api.extensions.ExtensionArray.shift

Problem description

pandas.api.extensions.ExtensionArray.view: Parameter "dtype" description should finish with "."
pandas.api.extensions.ExtensionArray.view: Return value has no description

pandas.api.extensions.ExtensionArray.fillna: Parameter "method" description should finish with "."
pandas.api.extensions.ExtensionArray.fillna: The first line of the returns section should contain only the type, unless multiple values are being returned
pandas.api.extensions.ExtensionArray.fillna: Return value has no description

pandas.api.extensions.ExtensionArray.shift: Parameter "fill_value" description should finish with "."
pandas.api.extensions.ExtensionArray.shift: The first line of the returns section should contain only the type, unless multiple values are being returned
pandas.api.extensions.ExtensionArray.shift: Return value has no description

This is a subset of #27977  and #28602