Fixes #46038

Mention Clone and refererences, and use more realistic examples (within
the constraints of a few lines :).

(Had to modify signature of `report_cannot_move_out_of` slightly to
satisfy requirements of newly added `fn cannot_move_out_of` method.)

No functional changes intended.

post-rebase: Do not put "(Ast)" suffix in error msg unless passed `-Z borrowck-mir`.
(But unconditionally include "(Mir)" suffix for mir-borrowck errors.)

After repatriating error explanations to the global registry, some lurking
doctest failures surfaced and needed to be chased down. Sadly, a few doctests
needed to be ignored due to a not-yet-understood regression in the doctest
`compile_fail` functionality (filed #43707).

Fixes #41139.

Fixes #30705

this makes sure the checks run before typeck (which might use the constant or const
function to calculate an array length) and gives prettier error messages in case of for
loops and such (since they aren't expanded yet).