perf pmu-events: Add API to get metric table name and iterate tables

perf pmu-events: Add API to get metric table name and iterate tables

Add name field to struct pmu_metrics_table and populate it in generated
tables. Add pmu_metrics_table__name() to retrieve the name. Add
pmu_metrics_table__for_each_table() to iterate over all known metric
tables.

This will be used to break apart slow metric tests per table.

Assisted-by: Gemini-CLI:Google Gemini 3
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>