Add 'use_debug_art' to product_variable

Add 'use_debug_art' property to product_variable so it can be checked
from Android.bp whether ART debug APEX or ART APEX should be used.

Bug: 351698657
Test: AOSP CF eng build succeeded
Test: AOSP CF userdebug build succeeded
Change-Id: I01cd80f0d899c55828ecb05fdafdc9bb05fd8200

android/config.go

@@ -2127,3 +2127,11 @@ func (c *config) BoardUseVbmetaDigestInFingerprint() bool {
 func (c *config) OemProperties() []string {
 	return c.productVariables.OemProperties
 }
+
+func (c *config) UseDebugArt() bool {
+	if c.productVariables.ArtTargetIncludeDebugBuild != nil {
+		return Bool(c.productVariables.ArtTargetIncludeDebugBuild)
+	}
+
+	return Bool(c.productVariables.Eng)
+}