Include flags files in product SBOM.

Bug: 272358980
Test: build/soong/tests/sbom_test.sh
Change-Id: Ifcb2f26044c346c54e60d1d4fb85fc4001f64210
diff --git a/core/packaging/flags.mk b/core/packaging/flags.mk
index 4b692be..cb43741 100644
--- a/core/packaging/flags.mk
+++ b/core/packaging/flags.mk
@@ -107,6 +107,7 @@
 		))
 
 ALL_DEFAULT_INSTALLED_MODULES += $(required_flags_files)
+ALL_FLAGS_FILES := $(required_flags_files)
 
 # TODO: Remove
 .PHONY: flag-files