simpleperf: report symbols of native libraries in apk file.

Changes included:
1. provide interface in read_apk.h to read build id and symbols.
2. report symbols of native libraries in apk file.
3. refactor code in read_elf.cpp and read_apk.cpp.
4. add verbose log.
5. add -o report_file_name option for report command.
6. add corresponding unit tests.

Bug: 26962895
Change-Id: I0d5398996e0c29dba4a6f5226692b758ca096bbd
diff --git a/simpleperf/dso.h b/simpleperf/dso.h
index a140e5e..9697319 100644
--- a/simpleperf/dso.h
+++ b/simpleperf/dso.h
@@ -93,6 +93,7 @@
   bool LoadKernel();
   bool LoadKernelModule();
   bool LoadElfFile();
+  bool LoadEmbeddedElfFile();
   void InsertSymbol(const Symbol& symbol);
   void FixupSymbolLength();