AAPT2: Parse coreApp in <manifest> as boolean

Bug:30751662
Change-Id: I283be5725426ee084944c1921df40d1bd6188028
diff --git a/tools/aapt2/link/XmlReferenceLinker.cpp b/tools/aapt2/link/XmlReferenceLinker.cpp
index 02af5e3..a29d8dc 100644
--- a/tools/aapt2/link/XmlReferenceLinker.cpp
+++ b/tools/aapt2/link/XmlReferenceLinker.cpp
@@ -126,8 +126,9 @@
                     mError = true;
 
                 }
-            } else {
-                // We still encode references.
+            } else if (!attr.compiledValue) {
+                // We still encode references, but only if we haven't manually set this to
+                // another compiled value.
                 attr.compiledValue = ResourceUtils::tryParseReference(attr.value);
             }