Add Windows UWP CI builders (#25498)

This enables Windows UWP builds in pre/post-submit.

ci/dev/prod_builders.json

@@ -68,6 +68,10 @@
          "name":"Windows Host Engine",
          "repo":"engine"
       },
+      {
+         "name":"Windows UWP Engine",
+         "repo":"engine"
+      },
       {
          "name":"Windows Web Engine",
          "repo":"engine"

ci/dev/try_builders.json

@@ -107,6 +107,11 @@
          "repo":"engine",
          "enabled": true
       },
+      {
+         "name":"Windows UWP Engine",
+         "repo":"engine",
+         "enabled": true
+      },
       {
          "name":"Windows Web Engine",
          "repo":"engine",