common: Support parsing in DecimalUnitFormat

common: Support parsing in DecimalUnitFormat

This allows parsing strings which represent a number with an optional
unit and SI-prefix, such as "1.2 kb" (1200), "1.2" (1.2), "1.2 m"
(0.0012), "12 ns" (0.000000012), etc.

Change-Id: Icd00870903bd22da6d322237ab1302276072217a
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/86097
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>