Also:
* improve the "ambiguous reference" error by swapping the order of
"declared here" and "also declared here" notes.
* improve the "not accessible from inner function" error:
- point out that it has to do with the thing being mutable
- eliminate the incorrect association with it being a function
- note where it crosses a namespace boundary
* struct field types are evaluated in a context that has the struct
namespace visible. Likewise with align expressions, linksection
expressions, enum tag values, and union/enum tag argument
expressions.
Closes#9194Closes#9622
4bb5d17edc