Robust and rationalized pass-through removal.

Phi input ordering is preserved by explicitly recording the states in which
an input is selected by the phi for a parameter in ContinuationInput::choose_in_states.

This is filled in using an initial FSM layout on the unoptimized continuation graph. Then, after optimization, the choose_in_states field is used to fill back in NewFSMState::current_inputs_by_input_param.

PiperOrigin-RevId: 889376624

Author: Sean Purser-Haskell

xls/contrib/xlscc/BUILD

@@ -195,6 +195,7 @@ cc_library(
         "//xls/ir:state_element",
         "//xls/ir:value",
         "//xls/ir:value_utils",
+        "@com_google_absl//absl/algorithm:container",
         "@com_google_absl//absl/container:btree",
         "@com_google_absl//absl/container:flat_hash_map",
         "@com_google_absl//absl/container:flat_hash_set",
@@ -257,6 +258,7 @@ cc_library(
         "//xls/passes:inlining_pass",
         "//xls/passes:node_source_analysis",
         "//xls/passes:optimization_pass",
+        "//xls/passes:optimization_pass_pipeline",
         "//xls/passes:partial_info_query_engine",
         "//xls/passes:pass_base",
         "//xls/solvers:z3_ir_translator",