This removes the filename from the file-scoped block, and places it
above to make it clear where the full SemIR begins (with multifile,
providing a barrier between).
This adds instructions so that we get printing. I may adjust the
instruction format a little further to add a type, but I think the basic
setup will remain.
Note this builds on #3414
This is an incremental improvement on our diagnostic messages that
simply underlines an entire token if the token is larger than 1 char
(else it points to the single char with a caret like it used to).
This should cover:
```
library "lib" api;
import Foo library default;
import library default;
import library "lib";
```
This splits out `PackageName` and `LibraryName` to their own parse nodes
so that checking can ignore them and still get a balanced parse tree
(otherwise, we essentially need to implement handling of the parse nodes
only to remove the identifiers/string literals -- the optional names
mean we can't blindly do that as before). For reference, these nodes
don't need to be handled because CheckParseTree will need to directly
funnel import information along with checked IRs.
As I was working on this, I noticed `import` and `library` syntax needs
to be fixed for how it imports the current package, and for `Main`
libraries. This mostly reflects the current state in its testing.
Otherwise, this should handle most of the errors I could think of:
dependency cycles, redundant imports, etc.
It does not actually deal with the nuances of cross-IR references.
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Jon Ross-Perkins
Jacob Schneider
