fix(to_cpp1): support initializing assignment from expression list in `operator=`

[JohelEGP]

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Resolves #679.

Testing summary:

100% tests passed, 0 tests failed out of 818

Total Test time (real) =  48.87 sec

Acknowledgements:

• Tested thanks to https://github.com/modern-cmake/cppfront.
• Commit messages follow Conventional Commits 1.0.0.
• Comments and commit messages follow Semantic Line Breaks.