A Variant shift multiplies a fractional value, and can return Empty #2437

Describe the bug
A Variant holding a Double, Currency or Decimal of 7.9, shifted left by 1, gives 15.8: the value is multiplied by 2, not shifted. Shifted right by 1, the Double and the Decimal give 3, but the Currency gives 3.95. A Variant holding an Integer or a Long shifted left by a count as large as the type's width gives Empty rather than 0. There is no diagnostic.

To Reproduce
Steps to reproduce the behavior:

1. Open variant-shift.twinproj (from variant-shift.zip) and run it (F5). Its Sub Main holds the whole bug:

   Dim d As Variant = CDbl(7.9)
   Dim c As Variant = CCur(7.9)
   Debug.Print d << 1            ' 15.8
   Debug.Print c >> 1            ' 3.95
   
   Dim i As Variant = CInt(1)
   Dim l As Variant = CLng(1)
   Debug.Print TypeName(i << 20) ' Empty
   Debug.Print TypeName(l << 32) ' Empty
   

2. See the DEBUG CONSOLE show 15.8, 3.95, Empty and Empty. The project prints the same for a Decimal too.

Expected behavior
A shift moves bits, so a fractional value should be truncated first, as the right shift of the Double and the Decimal already does: 7.9 << 1 is 14 and 7.9 >> 1 is 3. A count as large as the width of the type should give 0 and keep the type, as the Long variable's shift does, not Empty.

Desktop (please complete the following information):

• OS: Windows 10 Pro 22H2 (build 19045)
• twinBASIC compiler version: BETA 995

Additional context
Severity: wrong values, with no diagnostic. Also on BETA 983, with the same results, except that the right shift of a Variant holding 7.9 gave 4 there for all three types (BETA 984 made >> arithmetic). A Long variable's shift by 32 gives 0 on both builds.