[aapt2] Ensure all zip entry times are the same

We want them to be all the same, so that APKs are identical if its
contents are the same, regardless of the time zone of the machine that
produced them. The accompanying change in libziparchive
(Iefc7945bff0610f8a025d4887cd5644cfa3cfb3b) ensures this.

Bug: 277978832
Test: atest aapt2_tests
Change-Id: Iab000b7c74dcb06efad41a6495b73216fd2528d6
diff --git a/tools/aapt2/io/FileSystem.h b/tools/aapt2/io/FileSystem.h
index 0e798fc..f975196 100644
--- a/tools/aapt2/io/FileSystem.h
+++ b/tools/aapt2/io/FileSystem.h
@@ -32,6 +32,7 @@
   std::unique_ptr<IData> OpenAsData() override;
   std::unique_ptr<io::InputStream> OpenInputStream() override;
   const android::Source& GetSource() const override;
+  bool GetModificationTime(struct tm* buf) const override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(RegularFile);