provide xcode override method

.editorconfig

@@ -32,4 +32,7 @@ indent_style = space
 
 [*.plist]
 indent_size = 2
-indent_style = tab
+indent_style = tab
+
+[*.sh]
+end_of_line = lf

build/jobs/uno-uitest.yml

@@ -70,7 +70,7 @@ jobs:
 
 - job: UnoUITest_iOS
   displayName: Uno UITest iOS
-  condition: and(succeeded(), eq(variables['EnableUITest'], 'true'))
+  condition: and(succeeded(), eq(variables['EnableUITest'], 'true'), eq(variables['XcodeOverride'], ''))
   pool:
     vmImage: $(MacImage)
   workspace:

build/scripts/xcode-update.sh

@@ -0,0 +1,6 @@
+#!/bin/bash
+xcodeRoot=/Applications/Xcode_$XcodeOverride.app
+echo "Setting Xcode Override to: $xcodeRoot"
+
+echo '##vso[task.setvariable variable=MD_APPLE_SDK_ROOT;]'$xcodeRoot
+sudo xcode-select --switch $xcodeRoot/Contents/Developer

build/steps/set-runtime.yml

@@ -1,4 +1,12 @@
 steps:
+# For more information on what versions of Xcode are available see the following:
+# https://github.com/microsoft/azure-pipelines-image-generation/blob/master/images/macos/macos-10.15-Readme.md
+- script: build/scripts/xcode-update.sh
+  displayName: Force Xcode Update
+  env:
+    XcodeOverride: $(XcodeOverride)
+  condition: ne(variables['XcodeOverride'], '')
+
 - script: |
     dotnet tool install --global boots
     boots --stable Mono