Add missing FromExpr[BigDecimal] implementation

[jivanic-demystdata]

zio-prelude newtype implementation allows us to use macro to define newtype refinement based on any function:

// Refinement
object NotSoBigDecimalValidator
  extends Validator[BigDecimal]((v: BigDecimal) =>
    if (v.bigDecimal.toBigInteger.bitLength < 128) Right(())
    else Left(AssertionError.failure("NotSoBigDecimal cannot be be larger than 128 bits"))
  )

// newtype
type NotSoBigDecimal = NotSoBigDecimal.Type
object NotSoBigDecimal extends SubtypeCustom[BigDecimal] {
  override protected def validate(value: BigDecimal) = NotSoBigDecimalValidator.validate(value)
  inline override protected def validateInline(inline value: BigDecimal) = ${ NotSoBigDecimalValidator.validateInlineImpl('value) }
}

This code doesn't compile because the Validator is the following:

abstract class Validator[A: FromExpr](f: A => Either[AssertionError, Unit]) extends Liftables

But there's no instance of FromExpr for BigDecimal

Could be nice to add it to the language, don't you think? 🙂

Cc @guizmaii