shape_optimizer: dump GraphDef as .pbtxt before and after optimization pass

[Copilot]

Adds debug graph dumping to ShapeOptimizer::Optimize so the input and output GraphDef can be inspected as .pbtxt files around the optimization pass.

Changes

• shape_optimizer.cc: Include dump_graph.h and add two DumpGraphDefToFile calls guarded by VLOG_IS_ON(1):
  • Before optimization: dumps item.graph as before_ShapeOptimizer_<item.id>.pbtxt
  • After optimization: dumps *optimized_graph as after_ShapeOptimizer_<item.id>.pbtxt

Usage

# Write .pbtxt files to /tmp/graphs/
TF_DUMP_GRAPH_PREFIX=/tmp/graphs TF_CPP_MIN_VLOG_LEVEL=1 <your_binary>

# Or log graph text to stderr
TF_DUMP_GRAPH_PREFIX=- TF_CPP_MIN_VLOG_LEVEL=1 <your_binary>

item.id is used as the filename discriminator so before/after pairs are trivially correlated and multiple optimization runs don't collide. Follows the same pattern used in meta_optimizer.cc.