feat: improve constructor mapping readability

[aradalvand]

Fixes #1322

It's my first time contributing to a source generator project, so feel free to let me know if I've made any obvious mistakes.
Thanks.

Checklist

• The existing code style is followed
• The commit message follows our guidelines
• Performed a self-review of my code
• Hard-to-understand areas of my code are commented
• The documentation is updated (as applicable)
• Unit tests are added/updated
• Integration tests are added/updated (as applicable, especially if feature/bug depends on roslyn or framework version in use)

[latonz]

Thank you very much for this contribution! Since this is your first contribution I need to manually approve each GH Actions run...

Looks pretty good already 😊👍 I added my feedback, feel free to discuss. There are also a few test failures which need to be fixed.

[latonz]

Code looks good now, thanks for the updates 😊

There are still some test and linter failures which need to be fixed before merging.
See also linter failures, test failures.

[aradalvand]

@latonz Thanks! Sorry I've been very busy and couldn't get to fixing those, will do so this weekend when I hopefully get the time.