[iOS] Fix SkipOnCI attribute support on Apple mobile devices (#120671)

* Add DOTNET_CI environment variable to xharness command

* Refactor xharness command execution to conditionally set DOTNET_CI environment variable

* Update AOT build command to always set DOTNET_CI environment variable

* Add environment variable switches to xharness command in AOT build process

* Fix environment variable expansion in iOS build commands

* Test env variables

* Set HELIX_WORKITEM_ROOT env variable

Author: kotlarmilos

eng/testing/tests.ioslike.targets

@@ -33,7 +33,7 @@
     <_AfterBuildCommands>
       mv $XHARNESS_OUT/AOTBuild.binlog &quot;$HELIX_WORKITEM_UPLOAD_ROOT&quot;
       $(_AppleSignCommand)
-      xharness $(_AppleBuildCommand) --app &quot;$app&quot; --output-directory &quot;$output_directory&quot; --target &quot;$target&quot; --timeout &quot;$timeout&quot; --xcode &quot;$xcode_path&quot; -v --launch-timeout &quot;$launch_timeout&quot; $(_ResetSimulatorSwitch) $(_SignalAppEndSwitch) $(_AppleExpectedExitCode) -- </_AfterBuildCommands>
+      xharness $(_AppleBuildCommand) --app &quot;$app&quot; --output-directory &quot;$output_directory&quot; --target &quot;$target&quot; --timeout &quot;$timeout&quot; --xcode &quot;$xcode_path&quot; -v --launch-timeout &quot;$launch_timeout&quot; $(_ResetSimulatorSwitch) $(_SignalAppEndSwitch) $(_AppleExpectedExitCode) --set-env=HELIX_WORKITEM_ROOT=&quot;$HELIX_WORKITEM_ROOT&quot; -- </_AfterBuildCommands>
 
     <RunScriptCommand>$(_AOTBuildCommand) $(_AfterBuildCommands)</RunScriptCommand>
   </PropertyGroup>