Make the defaults property non-configurable

In order to support changing the global configuration per-module,
we can't make decisions on configuration until the configuration is
decided. The defaults mutator is one of the earliest mutators, and
it would be helpful to run it before deciding the configuration.

Bug: 361816274
Test: Presubmits
Change-Id: Iee9c603d7e2601919d636345dfdedae47448db38
diff --git a/android/module_test.go b/android/module_test.go
index 829c079..016fba3 100644
--- a/android/module_test.go
+++ b/android/module_test.go
@@ -722,6 +722,7 @@
 				propInfo{Name: "Arch.X86_64.A", Type: "string", Value: "x86_64 a"},
 				propInfo{Name: "B", Type: "bool", Value: "true"},
 				propInfo{Name: "C", Type: "string slice", Values: []string{"default_c", "c"}},
+				propInfo{Name: "Defaults", Type: "string slice", Values: []string{"foo_defaults"}},
 				propInfo{Name: "Embedded_prop", Type: "string", Value: "a"},
 				propInfo{Name: "Name", Type: "string", Value: "foo"},
 				propInfo{Name: "Nested.E", Type: "string", Value: "nested e"},