Fix the alloc error with enabled backtrace feature When angle_enable_unwind_backtrace_support is enabled, an assertion occurs on memory allocation with the following message: "constructed value does not match the lookup key" The assertion comes from PolicyTraits::apply() in the hash map. * In MemoryTracking.h, the type of mMemoryAllocationRecord is now std::unordered_map instead of angle::HashMap. Bug: b/262029018 Change-Id: I11a6d8e99a129759c046e37cef9e74f7db193066 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4289947 Reviewed-by: Charlie Lao <cclao@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com>