Use alternative format string specifier to ensure decimal point is present

[jkoritzinsky]

After this change, ildasm will generate the following:

.class public abstract auto ansi sealed beforefieldinit Program
       extends [System.Runtime]System.Object
{
  .field public static literal float64 ValueDoubleOne = float64(1.0000000000000000)
  .field public static literal float64 ValueDoubleOnePointTwo = float64(1.2000000000000000)
  .field public static literal float64 ValueDoubleMinusOne = float64(-1.0000000000000000)
  .field public static literal float64 ValueDoubleMinusZero = float64(-0.0000000000000000)
  .field public static literal float32 ValueFloatOne = float32(1.0000000)
  .field public static literal float32 ValueFloatOnePointTwo = float32(1.2000000)
  .field public static literal float32 ValueFloatMinusOne = float32(-1.0000000)
  .field public static literal float32 ValueFloatMinusZero = float32(-0.0000000)
} // end of class Program

Fixes #111014

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