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: Ic7c4a53d0df0cccd45eb699e236a92c8c0bc2d56
diff --git a/android/config.go b/android/config.go
index 3e7bb14..0b15c79 100644
--- a/android/config.go
+++ b/android/config.go
@@ -2081,3 +2081,7 @@
 func (c *config) GetApiLibraries() map[string]struct{} {
 	return c.apiLibraries
 }
+
+func (c *deviceConfig) CheckVendorSeappViolations() bool {
+	return Bool(c.config.productVariables.CheckVendorSeappViolations)
+}