DataGridNumericUpDownColumn doesn't has a TextAlignment

[ahmediddma]

Describe the bug
the DataGridNumericUpDownColumn doesn't has TextAlignment property and it's content will always be in the left side even if the flow direction is RightToLeft

To Reproduce
just make the Datagrid in the demo app flow direction RightToLeft then check the content in the DataGridNumericUpDownColumn there.

Expected behavior
the TextAlignment should be added
if the flow direction is right to left the default for start typing should be on the right side of the controller as well

Screenshots

Environment(please complete the following information):

• MahApps.Metro version [1.6.5]
• OS: [Win10 1903]
• Visual Studio [2019 latest stable one]
• .NET Framework [4.7.2]