Fix & fuzz ZSTD_generateSequences

This function was seriously flawed:
* It didn't do output bounds checks
* It produced invalid sequences when an uncompressed or RLE block was emitted
* It produced invalid sequences when the block splitter was enabled
* It produced invalid sequences when ZSTD_c_targetCBlockSize was enabled

I've attempted to fix these issues, but this function is just a bad idea,
so I've marked it as deprecated and unsafe. We should replace it with
`ZSTD_extractSequences()` which operates on a compressed frame.

tests/fuzz/Makefile

@@ -125,7 +125,8 @@ FUZZ_TARGETS :=       \
 	seekable_roundtrip \
 	huf_round_trip \
 	huf_decompress \
-	decompress_cross_format
+	decompress_cross_format \
+	generate_sequences
 
 all: libregression.a $(FUZZ_TARGETS)
 
@@ -239,10 +240,13 @@ huf_round_trip: $(FUZZ_HEADERS) $(FUZZ_ROUND_TRIP_OBJ) rt_fuzz_huf_round_trip.o
 
 huf_decompress: $(FUZZ_HEADERS) $(FUZZ_DECOMPRESS_OBJ) d_fuzz_huf_decompress.o
 	$(CXX) $(FUZZ_TARGET_FLAGS) $(FUZZ_DECOMPRESS_OBJ) d_fuzz_huf_decompress.o $(LIB_FUZZING_ENGINE) -o $@
-	
+
 decompress_cross_format: $(FUZZ_HEADERS) $(FUZZ_DECOMPRESS_OBJ) d_fuzz_decompress_cross_format.o
 	$(CXX) $(FUZZ_TARGET_FLAGS) $(FUZZ_DECOMPRESS_OBJ) d_fuzz_decompress_cross_format.o $(LIB_FUZZING_ENGINE) -o $@
 
+generate_sequences: $(FUZZ_HEADERS) $(FUZZ_ROUND_TRIP_OBJ) rt_fuzz_generate_sequences.o
+	$(CXX) $(FUZZ_TARGET_FLAGS) $(FUZZ_ROUND_TRIP_OBJ) rt_fuzz_generate_sequences.o $(LIB_FUZZING_ENGINE) -o $@
+
 libregression.a: $(FUZZ_HEADERS) $(PRGDIR)/util.h $(PRGDIR)/util.c d_fuzz_regression_driver.o
 	$(AR) $(FUZZ_ARFLAGS) $@ d_fuzz_regression_driver.o