spirv-reader: Add method to be used in tests later

Bug: tint:508
Change-Id: Ifd83bcfe168a2be0a11e8a81e392ba20101fc586
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48865
Auto-Submit: David Neto <dneto@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/reader/spirv/parser_impl.h

@@ -507,6 +507,12 @@ class ParserImpl : Reader {
     return 0;
   }
 
+  /// @param entry_point the SPIR-V ID of an entry point.
+  /// @returns the entry point info for the given ID
+  const std::vector<EntryPointInfo>& GetEntryPointInfo(uint32_t entry_point) {
+    return function_to_ep_info_[entry_point];
+  }
+
  private:
   /// Converts a specific SPIR-V type to a Tint type. Integer case
   sem::Type* ConvertType(const spvtools::opt::analysis::Integer* int_ty);