Uncouple doctype transformation

[lagru]

This refactor uncouples the doctype transformation. Structure information from parsing is preserved as much as possible so that it can be later used during name resolution. The end goal here is to eventually allow caching of the transformation. Since that is pretty independent of configuration or context.

This also addresses a few gaps in the grammar.

Release notes

For maintainers and optionally contributors, please refer to the instructions on how to document this PR for the release notes.

Uncouple doctype transformation from name resolution.
{label="maintenance"}

Add support for expressions like `Literal[1, "some string"]` in doctypes.
The grammar previously only allowed names inside this form.
{label="bug fix"}

Log warnings emitted while parsing docstrings with NumPyDoc
and link to the file and line number of the docstring.
{label="enhancement"}