[mlir] Elide large elements attrs when printing Operations in diagnostics

Diagnostics are intended to be read by users, and in most cases displayed in a terminal. When not eliding huge element attributes, in some cases we end up dumping hundreds of megabytes(gigabytes) to the terminal (or logs), completely obfuscating the main diagnostic being shown.

Differential Revision: https://reviews.llvm.org/D102272