- Eliminate unconditional heap reads in tracing code.
- Change operator<< on ObjectRef to additionally print
  the Brief() output when the broker is disabled.
- Print line number in TRACE_BROKER_MISSING and make
  some messages more consistent.
- Make PrintCandidates output clearer.
- Be more consistent about dereferencing optionals.

Bug: v8:7790, chromium:990478
Change-Id: I2917529d5138a0d63ad476d3f8fee6a963767b23
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1758311
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63242}