Improve diagnostic when emitting operations with regions

This has a broad impact on diagnostics that attach an operation. Ops
with one or more regions will now be printed on a new line. It was
confusing and hard to read with a trailing first line for ops
with regions.

Before:

```
<unknown>:0: note: see current operation: affine.for %arg3 = 0 to 8192 {
  affine.for %arg4 = 0 to 8192 step 512 {
    affine.for %arg5 = 0 to 8192 step 128 {

    ...
```

After:

```
<unknown>:0: note: see current operation:
affine.for %arg3 = 0 to 8192 {
  affine.for %arg4 = 0 to 8192 step 512 {
    affine.for %arg5 = 0 to 8192 step 128 {
      ...
```

Differential Revision: https://reviews.llvm.org/D132645