If a symbol name can only be imported from one place for a type, and
as long as it was not glob-imported anywhere in the current crate, we
can trim its printed path and print only the name.
This has wide implications on error messages with types, for example,
shortening `std::vec::Vec` to just `Vec`, as long as there is no other
`Vec` importable anywhere.
This adds a new '-Z trim-diagnostic-paths=false' option to control this
feature.
On the good path, with no diagnosis printed, we should try to avoid
issuing this query, so we need to prevent trimmed_def_paths query on
several cases.
This change also relies on a previous commit that differentiates
between `Debug` and `Display` on various rustc types, where the latter
is trimmed and presented to the user and the former is not.
When an error occurs due to a partial move, we would use the world
"partial" in some parts of the error message, but not in others. This
commit ensures that we use the word 'partial' in either all or none of
the diagnostic messages.
Additionally, we no longer describe a move out of a `Box` via `*` as
a 'partial move'. This was a pre-existing issue, but became more
noticable when the word 'partial' is used in more places.
