Provide a way to sort one single resx file

**Is your feature request related to a problem? Please describe.**
Having sort enabled on save breaks the winforms designer.
I have to save after each modification in the form to be sure to not lose all modifications since the previous save.
It makes the designer experience very unfriendly.
It looks similar to an issue in [CodeMaid ](https://github.com/codecadwallader/codemaid/issues/180)and I narrowed it to ResxResourceManager (I suspected Resharper)

**Describe the solution you'd like**
I would like to sort a given file using a context menu (below "Open ResX Manager" ?).

**Describe alternatives you've considered**
"Sort all files" command is not desired as it modified all the resx files within my solution (which is quite big)