refactor(absl): Use the abseil in thirdparty instead of the internal copied one

[acelyc111]

For historical reasons, we copied some Abeil-cpp code into Pegasus to use
features like string_view, make_unique, apply and etc. The Abeil library
has been introduced into Pegasus as a thirdparty in previous patches, so
we can use it directly.
This patch has the following changes:

• Remove the abseil files copied to Pegasus including:
  • src/utils/absl/base/internal/invoke.h
  • src/utils/absl/utility/utility.h
  • src/utils/memutil.h
  • src/utils/smart_pointers.h
  • src/utils/string_view.cpp
  • src/utils/string_view.h
  • src/utils/test/memutil_test.cpp
  • src/utils/test/smart_pointers_test.cpp
  • src/utils/test/string_view_test.cpp
• Update license related files(.licenserc.yaml and LICENSE)
• Use std::make_unique explicitly.
• Add a function to_string_view(), then dsn::blob is possible to
  transfer to absl::string_view.

[neverchanje]

lol It was the old time practice to use abseil. I recalled that abseil would introduce some compiler errors at the time I tried to use it. Good to hear that you decided to fully integrate it.