Changes imported from Abseil "staging" branch:

  - 55a89fda61ddf8aa76d0a3b6bc44bf6b5b6eadfc Internal cleanup by Abseil Team <absl-team@google.com>
  - b7646f979ee40c5716833692f2eb24b8058cf4c8 Internal cleanup by Gennadiy Rozental <rogeeff@google.com>
  - 12a4051b0ea91c6a6211f738fa24e1bc7064c09a Merging changes from https://github.com/abseil/abseil-cpp... by Daniel Katz <katzdm@google.com>
  - 2e259588d62118a70837a3d8408cb6c763f48420 Replace EXPECT_TRUE(StrContains(...)) with an assert exam... by Abseil Team <absl-team@google.com>
  - 8f7d251b3486f2b03dc712ad0822b9dc87a7964b Make Uint128(High|Low)64 constexpr. by Alex Strelnikov <strel@google.com>
  - 955fd38a23896e003105defc0ef221a2c10d392e Internal change by Jon Cohen <cohenjon@google.com>

GitOrigin-RevId: 55a89fda61ddf8aa76d0a3b6bc44bf6b5b6eadfc
Change-Id: Ia062fe8a0559aa3ace3736d2a53f6da13af40b2c