migrate to new api of abseil-cpp

[fundawang]

abseil/abseil-cpp@caf854d#diff-a84ab48de639246d3e520df4c5ea31d325b4e5bd473cd4a8beec558712d06d48

abseil-cpp has deprecated template type alias nullability annotations in May 2025, and remove in Aug 2025. If trying to build autofdo with new abseil-cpp put into thirdparty, it fails with:

In file included from /home/lkp/rpmbuild/BUILD/autofdo-0.30.1/mini_disassembler.cc:1:
/home/lkp/rpmbuild/BUILD/autofdo-0.30.1/mini_disassembler.h:26:31: error: 'Nonnull' is not a member of 'absl'
   26 |   static absl::StatusOr<absl::Nonnull<std::unique_ptr<MiniDisassembler>>>
      |                               ^~~~~~~
/home/lkp/rpmbuild/BUILD/autofdo-0.30.1/mini_disassembler.h:26:71: error: template argument 1 is invalid
   26 |   static absl::StatusOr<absl::Nonnull<std::unique_ptr<MiniDisassembler>>>
      |                                                                       ^~
/home/lkp/rpmbuild/BUILD/autofdo-0.30.1/mini_disassembler.h:26:73: error: expected unqualified-id before '>' token
   26 |   static absl::StatusOr<absl::Nonnull<std::unique_ptr<MiniDisassembler>>>
      |                                                                         ^
/home/lkp/rpmbuild/BUILD/autofdo-0.30.1/mini_disassembler.cc:27:22: error: 'Nonnull' is not a member of 'absl'
   27 | absl::StatusOr<absl::Nonnull<std::unique_ptr<MiniDisassembler>>>
      |                      ^~~~~~~
/home/lkp/rpmbuild/BUILD/autofdo-0.30.1/mini_disassembler.cc:27:62: error: template argument 1 is invalid
   27 | absl::StatusOr<absl::Nonnull<std::unique_ptr<MiniDisassembler>>>
      |                                                              ^~
/home/lkp/rpmbuild/BUILD/autofdo-0.30.1/mini_disassembler.cc:27:64: error: expected unqualified-id before '>' token
   27 | absl::StatusOr<absl::Nonnull<std::unique_ptr<MiniDisassembler>>>