Revise Flatbuffers codegen style (#7964)

* Rename the generated Flatbuffer headers

The Blaze/Bazel rules for Flatbuffers are inflexible and require this naming pattern :-/

* Also update the flags to flatc

* Fix lots of stuff

* exclude from clang-format

* ignore again

.clang-format-ignore

@@ -15,3 +15,4 @@
 # mini_webgpu.h is copied from upstream with some local mods
 ./src/runtime/mini_webgpu.h
 ./dependencies/spirv
+*.fbs.h

Makefile

@@ -1395,14 +1395,14 @@ $(BIN_DIR)/test_internal: $(ROOT_DIR)/test/internal.cpp $(BIN_DIR)/libHalide.$(S
 	$(CXX) $(TEST_CXX_FLAGS) $< -I$(SRC_DIR) $(TEST_LD_FLAGS) -o $@
 
 ifneq (,$(shell which flatc))
-$(BUILD_DIR)/Deserialization.o : $(BUILD_DIR)/halide_ir_generated.h
-$(BUILD_DIR)/Serialization.o : $(BUILD_DIR)/halide_ir_generated.h
+$(BUILD_DIR)/Deserialization.o : $(BUILD_DIR)/halide_ir.fbs.h
+$(BUILD_DIR)/Serialization.o : $(BUILD_DIR)/halide_ir.fbs.h
 endif
 
 # Generated header for serialization/deserialization
-$(BUILD_DIR)/halide_ir_generated.h: $(SRC_DIR)/halide_ir.fbs
+$(BUILD_DIR)/halide_ir.fbs.h: $(SRC_DIR)/halide_ir.fbs
 	@mkdir -p $(@D)
-	flatc -o $(BUILD_DIR) -c $^  
+	flatc --cpp --cpp-std C++17 --no-union-value-namespacing --keep-prefix --filename-suffix ".fbs" -o $(BUILD_DIR) $^
 
 # Correctness test that link against libHalide
 $(BIN_DIR)/correctness_%: $(ROOT_DIR)/test/correctness/%.cpp $(BIN_DIR)/libHalide.$(SHARED_EXT) $(INCLUDE_DIR)/Halide.h $(RUNTIME_EXPORTED_INCLUDES)