perf test: Add file offset diagnostic test for corrupted perf.data

perf test: Add file offset diagnostic test for corrupted perf.data

Add a shell test that verifies the file_offset diagnostic messages
work correctly when perf encounters corrupted events.

The test corrupts a MMAP2 event's size field in a recorded perf.data
file, then checks that perf report produces warning messages that
include both the file offset (e.g. "at offset 0x2738:") and the
event type name with numeric id (e.g. "MMAP2 (10)").

This exercises the diagnostic improvements from the file_offset
series, which retrofitted all skip/stop/error messages to include
the position and type of the problematic event.

Reviewed-by: Ian Rogers <irogers@google.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>