opt: estimate cost of both Hufman and FSE symbols

For FSE symbols : provide an upper bound,
in nb of bits,
since cost function is not able to store fractional bit costs.

lib/common/fse.h

@@ -575,6 +575,12 @@ MEM_STATIC void FSE_flushCState(BIT_CStream_t* bitC, const FSE_CState_t* statePt
     BIT_flushBits(bitC);
 }
 
+MEM_STATIC U32 FSE_getMaxNbBits(const FSE_symbolCompressionTransform* symbolTT, U32 symbolValue)
+{
+    assert(symbolValue <= FSE_MAX_SYMBOL_VALUE);
+    return (symbolTT[symbolValue].deltaNbBits + ((1<<16)-1)) >> 16;
+}
+
 
 /* ======    Decompression    ====== */