[cfe] Implement constructor tearoffs support in the CFE

[eernstg]

This issue tracks support of the constructor tearoffs feature. See the enclosing meta-issue for details.

[eernstg]

NB: One part of this feature has not yet been implemented, I created #47147 in order to handle that.

[eernstg]

@stefantsov, I thought about reopening this issue instead, please do that if needed.

[johnniwinther]

This seems to be complete.