Use board api level for seapp coredomain check

Rather than PRODUCT_SHIPPING_API_LEVEL, use board api level
(BOARD_API_LEVEL or BOARD_SHIPPING_API_LEVEL) to determine whether we
check coredomain violations or not.

Also provides a Makefile variable to override the flag, for targets that
want to turn on the check optionally.

Bug: 280547417
Test: see build command of vendor_seapp_contexts
Change-Id: I177630d33313334ca4a56a9be88b78cff678281e
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 26998ed..7d8092d 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -324,6 +324,8 @@
 
 $(call add_json_bool, KeepVndk, $(filter true,$(KEEP_VNDK)))
 
+$(call add_json_bool, CheckVendorSeappViolations, $(filter true,$(CHECK_VENDOR_SEAPP_VIOLATIONS)))
+
 $(call json_end)
 
 $(file >$(SOONG_VARIABLES).tmp,$(json_contents))