AAPT2: optionally keep resources without default value

Teach "aapt2 link" about a new flag --no-resource-removal. When given,
aapt2 will not filter out resources that lack default values. This is
useful mostly when building overlay packages that define resources for
non-default configurations, such as only for values-sv.

Test: manual: build package with resource only in values-vs, verify apk with aapt2 dump
Change-Id: Idc513bcb3f43bbff7f073163562c3dfccdb9bc9b
diff --git a/tools/aapt2/cmd/Link.cpp b/tools/aapt2/cmd/Link.cpp
index 20ea3cb6..8666f7b 100644
--- a/tools/aapt2/cmd/Link.cpp
+++ b/tools/aapt2/cmd/Link.cpp
@@ -1775,10 +1775,12 @@
 
     // Before we process anything, remove the resources whose default values don't exist.
     // We want to force any references to these to fail the build.
-    if (!NoDefaultResourceRemover{}.Consume(context_, &final_table_)) {
-      context_->GetDiagnostics()->Error(DiagMessage()
-                                        << "failed removing resources with no defaults");
-      return 1;
+    if (!options_.no_resource_removal) {
+      if (!NoDefaultResourceRemover{}.Consume(context_, &final_table_)) {
+        context_->GetDiagnostics()->Error(DiagMessage()
+                                          << "failed removing resources with no defaults");
+        return 1;
+      }
     }
 
     ReferenceLinker linker;