export complete package names (including features)

[dimbleby]

I have in mind a fix to python-poetry/poetry#5537 such that the packages returned by get_project_dependency_packages() include any features that ought to be installed.

Then this fix will cause those features to be included at export.

(Except for local dependencies, which I suppose would need some different fix. I don't intend to do anything about that in this MR: it's getting a touch complicated and I don't myself care about exporting requirements.txt for local dependencies).

[sonarcloud]

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[dimbleby]

The plan that I outline only works if #64 is also merged, else we fall foul of

poetry-plugin-export/src/poetry_plugin_export/exporter.py

Lines 118 to 119 in db1db23

	if package not in packages:
	continue

- which is what caused me to make that MR in the first place