Fix error with new stop command pausing silos

[lL1l1]

Issue

IssueUnitCommand was being given a UserUnit instead of a UserUnit[] in the new behavior from #6557, causing the following error:

WARNING: Error running HandleEvent script in CScriptObject at 19c8a700: ...rs\colon3\documents\github\fa\lua\ui\game\orders.lua(332): Expected a game object. (Did you call with '.' instead of ':'?)
         stack traceback:
         	[C]: in function `IssueUnitCommand'
         	...rs\colon3\documents\github\fa\lua\ui\game\orders.lua(332): in function `Stop'
         	...rs\colon3\documents\github\fa\lua\ui\game\orders.lua(355): in function `OnClick'
         	...ers\colon3\documents\github\fa\lua\maui\checkbox.lua(143): in function `HandleEvent'
         	...rs\colon3\documents\github\fa\lua\ui\game\orders.lua(1303): in function <...rs\colon3\documents\github\fa\lua\ui\game\orders.lua:1281>

Description of the proposed changes

• Like was done for a few other User functions, add a single unit version of IssueUnitCommand.
  • Use this new function in the stop order behavior to correctly issue the pause order to the silos.
• Fix the shift version of stop not using the new stop behavior.
• related annotations

Testing done on the proposed changes

Spawn some silos and make sure the stop command and its shift version work

   CreateUnitAtMouse('xsb2108', 0,    0.00,   -2.00, -0.00000)
   CreateUnitAtMouse('xsb2108', 0,    0.00,    0.00, -0.00000)
   CreateUnitAtMouse('xsb2108', 0,    0.00,    2.00, -0.00000)

Checklist

• Changes are annotated, including comments where useful
• Changes are documented in the changelog for the next game version