fix: lower (nested) _braced-init-list_ (argument)

[JohelEGP]

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Resolves #1283. Resolves #1037. Resolves #568. Resolves #542.

The main branch already treats a return type contextually, only lowering a braced-init-list if it can work: https://cpp2.godbolt.org/z/sonKE4zan.

This PR recognizes two other places where an expression list can be an initializer to lower as a braced-init-list:

• As a function argument.
• As an expression in the expression list of an initializer (nested braced-init-list).