Cut the multiproduct_kati -> soong-ui-build dep.

This is done by moving SetupSignals() to its own little package.

There are a number of tiny little utility packages for soong_ui we might
be better of merging, but that's for another change (maybe)

Test: Presubmits.
Change-Id: I07b0ca98bfb8884ef4223d665e632183b9896a0d

cuj/Android.bp

@@ -7,6 +7,7 @@ blueprint_go_binary {
     deps: [
         "soong-ui-build",
         "soong-ui-logger",
+        "soong-ui-signal",
         "soong-ui-terminal",
         "soong-ui-tracer",
     ],