lower: diagnose passing a by-ref loop capture where a value is expected

`for xs: (*m)` binds `m` to a `*T`. Passing it directly to a parameter
that wants `T` produced invalid IR that only LLVM's verifier caught, with
the opaque 'Call parameter type does not match function signature'. Detect
it at the call site and emit a clear error with a fix-it suggesting `m.*`.

Add example 215 + expected output as a regression test.

tests/expected/215-ref-capture-value-arg-diagnostic.exit

@@ -0,0 +1 @@
+1