Add the C API tests for Mapping Protocol and Sequence Protocol

[serhiy-storchaka]

Currently only few functions in these protocols are covered by tests: PyMapping_Keys, PyMapping_Values, PyMapping_Items, PyMapping_HasKey, PyMapping_HasKeyString, PySequence_SetSlice, PySequence_DelSlice. Since we just added few new functions (PyMapping_GetOptionalItem, etc) and are planning to deprecate other functions (PyMapping_HasKey, etc), we need more tests.

Linked PRs

• gh-107178: Add the C API tests for the Abstract Objects Layer #107179
• [3.12] gh-107178: Add the C API tests for the Abstract Objects Layer (GH-107179) #107728
• gh-107178: Remove _testcapi.test_dict_capi() #108436