Make aapt2 terminology more inclusive

Update language to comply with Android's inclusive language guidance

See https://source.android.com/setup/contribute/respectful-code
for reference

Bug: 162364131
Bug: 162536543
Test: aapt2_tests
Change-Id: I4eef925d6319b40a395fc8d59a3f2912a02ca03b
diff --git a/tools/aapt2/link/TableMerger.h b/tools/aapt2/link/TableMerger.h
index a35a134..e01a0c1 100644
--- a/tools/aapt2/link/TableMerger.h
+++ b/tools/aapt2/link/TableMerger.h
@@ -80,9 +80,9 @@
   DISALLOW_COPY_AND_ASSIGN(TableMerger);
 
   IAaptContext* context_;
-  ResourceTable* master_table_;
+  ResourceTable* main_table_;
   TableMergerOptions options_;
-  ResourceTablePackage* master_package_;
+  ResourceTablePackage* main_package_;
   std::set<std::string> merged_packages_;
 
   bool MergeImpl(const Source& src, ResourceTable* src_table, bool overlay, bool allow_new);