Generic ItemDefinition parametrization protocol (#3926)

[RonnyPfannschmidt]

Note

Stack: #14855 -> #14856 -> #14769 -> #14857 -> #14858. Top of the chain.
Review only the last commit.

Gives nodes.ItemDefinition the collect() protocol, so a non-Python collector
can have its test definitions parametrized through pytest_generate_tests:

class YamlDefinition(nodes.ItemDefinition):
    parametrize_argnames = ("value",)

    def make_item(self, parent, *, name, callspec, nodeid, context):
        return YamlItem.from_parent(
            parent, name=name, nodeid=nodeid, spec=dict(callspec.params)
        )

Ids, pytest.param(...) marks and node-id selection work as they do for Python
tests. Attaching the callspec, its marks and its id to the generated item is done
by the protocol rather than left to each make_item() — the callspec drives
reordering and high-scoped param caching, so it is not optional.

ParametrizeContext moves into _pytest.parametrize as the collector-agnostic
base of Metafunc, which overrides four seams (_infer_scope,
_validate_argnames, _register_direct_params, _introspection_target).

Not included: fixture resolution for non-Python items — no indirect=True,
no scope inference, no requesting fixtures.
doc/en/proposals/generic_fixture_closures.rst writes up the four couplings in
the way and a three-step path.

Requires #14855: test_ids_and_marks_from_pytest_param hits the skip-location
INTERNALERROR without it. Relevant if the chain is reordered.