Also, restructure the `CHECK:` lines for the `-emit-tbd` test. The number of
columns in the `.tbd` file appears to be variable, so we can't assume a layout
for the symbols in the YAML.
Type-checking patterns is not fully requestified, so the
ASTPrinter should not assume this has been filled in.
It appears sufficient to just visit the associated VarDecl,
as we do already.
Experimental mode for generating module interfaces without running
primary file type-checking. The idea is that the ASTPrinter triggers
requests to only do the minimum amount of type checking work
possible while printing the interface for a module's public
declarations.
These requests may emit diagnostics, but the ASTPrinter should in
theory already be robust against invalid code.
