Add support for target typed conditional expression

[RexJaeschke]

12.18 Conditional operator has an open issue; see the following words in that section: placeholder for words somehow referring to “12.6.4.5 Better conversion from expression.”

Here are the details:

Mail to Bill on 2024-03-18: The MS spec suggests the text for “12.6.4.5 Better conversion from expression” be augmented; OK. However, “12.18 Conditional operator“ does not reference that section; instead, it points to “12.6.3.15 Finding the best common type of a set of expressions.” So, I don’t see how the proposed changes to “better conversion” will be seen in the context of “best common type.” Unless these two are somehow linked and I’m not seeing where.

Bill’s reply on 2024-04-01: I think the conditional expression section should reference both sections, as sometimes the conditional expression applies when there is no best common type.