Print out large elementsattr's such that they are parseable.

I found that when running crash reproducers, the elided elementsattr's
would prevent parsing the IR repro. I found myself manually going and
replacing the "..." with some valid IR.

With this change, we now print elided attrs as `opaque<"", "0xDEADBEEF">`
to clearly delineate them as being elided while still being parseable.

PiperOrigin-RevId: 283781806