trace_processor: add template substitution support for SQL metrics

Also implement the basic process counter metrics to prove the concept.

Context: go/perfetto-metrics
Bug: 129747127
Change-Id: Ia9304328f6368bca085135fac0178243ffc0d9df
diff --git a/Android.bp b/Android.bp
index 62bf1cf..3544957 100644
--- a/Android.bp
+++ b/Android.bp
@@ -19,6 +19,7 @@
   srcs: [
     "src/trace_processor/metrics/android/android_mem.sql",
     "src/trace_processor/metrics/android/android_mem_lmk.sql",
+    "src/trace_processor/metrics/android/android_mem_proc_counters.sql",
   ],
   cmd: "$(location tools/gen_merged_sql_metrics.py) --cpp_out=$(out) $(in)",
   out: [