processor: Extract generations of incremental state into helper class

Adds a PacketSequenceStateGeneration class, which effectively
encapsulates the state pointer and generation data into a single object.

This way, it's possible to store a single pointer in
TimestampedTracePiece, rather than a pointer and index.

Bug: 123864183, 142557489
Change-Id: I14fd3d97ca67fb2ddaa33b23d4f28c4563affa41
diff --git a/Android.bp b/Android.bp
index 9a0c021..40693fa 100644
--- a/Android.bp
+++ b/Android.bp
@@ -5812,6 +5812,7 @@
     "src/trace_processor/importers/fuchsia/fuchsia_trace_tokenizer.cc",
     "src/trace_processor/importers/fuchsia/fuchsia_trace_utils.cc",
     "src/trace_processor/importers/proto/args_table_utils.cc",
+    "src/trace_processor/importers/proto/packet_sequence_state.cc",
     "src/trace_processor/importers/proto/proto_importer_module.cc",
     "src/trace_processor/importers/proto/proto_trace_parser.cc",
     "src/trace_processor/importers/proto/proto_trace_tokenizer.cc",