Move [expected] from [utilities] to [diagnostics]

The [utilties] clause should be a clause of last resort, when no other clause makes sense. Additionally, the [utilties] clause has historically been one of the larger clauses.

I recommend moving [expected] from [utilities] to [diagnostics]. std::expected is a tool most frequently used for error handling, so placing it in the same clause that we use to discuss errno and terminate makes sense.

Without this change, [diagnostics] is roughly 20 pages in N4928 and [utilities] is roughly 145 pages. Moving [expected] can shift ~31 pages from [utilities] to [diagnostics].

The header table in each clause would need to be adjusted. Other than that, I didn't see any blanket wording in [utilities] that needs to be moved or duplicated into [diagnostics]. [diagnostics.general] p2 may need a minor tweak to describe std::expected.

Locate the [expected], [utilities], and [diagnostics] clauses in the draft, along with their header tables and [diagnostics.general] p2. Review how clause organization and cross-references are represented, then move [expected] and adjust the two header tables and any needed wording. Done means the clause contents and page organization reflect the proposed placement without unintended changes.