Run rustfmt on tests/codegen/.

Except for `simd-intrinsic/`, which has a lot of files containing
multiple types like `u8x64` which really are better when hand-formatted.

There is a surprising amount of two-space indenting in this directory.

Non-trivial changes:
- `rustfmt::skip` needed in `debug-column.rs` to preserve meaning of the
  test.
- `rustfmt::skip` used in a few places where hand-formatting read more
  nicely: `enum/enum-match.rs`
- Line number adjustments needed for the expected output of
  `debug-column.rs` and `coroutine-debug.rs`.

rustfmt.toml

@@ -14,7 +14,7 @@ ignore = [
     # - some contain syntax errors that cause rustfmt to give an error
     # - some UI tests are broken by different formatting
     # - some require special comments in a particular position (e.g. `EMIT_MIR` comments)
-    "/tests/codegen/",
+    "/tests/codegen/simd-intrinsic/", # Many types like `u8x64` are better hand-formatted.
     "/tests/codegen-units/",
     "/tests/coverage/",
     "/tests/coverage-run-rustdoc/",