Support `use_d8` partial compile flag

Make `use_d8` an opt-out flag (when SOONG_PARTIAL_COMPILE=true).

Bug: b/374975543
Test: manual, TH
Change-Id: Iaef4bb5243957812783c5dbc79a5bf27e1096166
diff --git a/android/config_test.go b/android/config_test.go
index 4bdf05f..3d86860 100644
--- a/android/config_test.go
+++ b/android/config_test.go
@@ -239,10 +239,10 @@
 	}{
 		{"", true, defaultPartialCompileFlags},
 		{"false", true, partialCompileFlags{}},
-		{"true", true, defaultPartialCompileFlags.updateEnabled(true)},
+		{"true", true, enabledPartialCompileFlags},
 		{"true", false, partialCompileFlags{}},
-		{"true,use_d8", true, defaultPartialCompileFlags.updateEnabled(true).updateUseD8(true)},
-		{"true,-use_d8", true, defaultPartialCompileFlags.updateEnabled(true).updateUseD8(false)},
+		{"true,use_d8", true, enabledPartialCompileFlags.updateUseD8(true)},
+		{"true,-use_d8", true, enabledPartialCompileFlags.updateUseD8(false)},
 		{"use_d8,false", true, partialCompileFlags{}},
 		{"false,+use_d8", true, partialCompileFlags{}.updateUseD8(true)},
 	}