BigDecimalFromDigits unused for generic literals with exponents

[bishabosha]

minimized code

scala> 1e500: BigDecimal                                                                                                       
1 |1e500: BigDecimal
  |^^^^^
  |number too large

expectation

scala> 1e500: BigDecimal                                                                                                                           
val res0: BigDecimal = 1E+500