Add parser for EROFS file data

This CL parses file names and compression info from input EROFS image,
so that OTA generation can use it later.

Test: th
Test: Generate an incremental OTA with erofs images, make sure we see
file lists.
Bug: 206729162

Change-Id: I70536d7762acc19a6977460738065d5557338532
diff --git a/lz4diff/lz4diff_format.h b/lz4diff/lz4diff_format.h
index 5b5ce40..9875c12 100644
--- a/lz4diff/lz4diff_format.h
+++ b/lz4diff/lz4diff_format.h
@@ -58,8 +58,12 @@
 };
 
 struct CompressedFile {
+  // Extents in this array should be in range [0, file_size]. It represents
+  // which bytes inside this file are compressed. Useful for compressed file
+  // systems like EROFS.
   std::vector<CompressedBlock> blocks;
   CompressionAlgorithm algo;
+  // Whether the EROFS zero padding feature is enabled
   bool zero_padding_enabled{};
 };