Changes imported from Abseil "staging" branch:

  - 989557e6b443a81b5ad9bd0d0c704edbe96c09c9 Make InlinedVector::ShiftRight update the vector's size -... by Jon Cohen <cohenjon@google.com>
  - ffc2e2a6f169bbfa823890f21d13e16110cd0206 Fix issues when passing references aliasing into an Inlin... by Jon Cohen <cohenjon@google.com>
  - 2fce2f87043f8c044889b4aab828e6edc20da0d9 In C++14 or later, alias absl::make_unique to std::make_u... by Abseil Team <absl-team@google.com>
  - cb83e95b486c59fd6acfa956e97f42253dd158bd Roll back change to avoid weak virtual table warnings (-W... by Abseil Team <absl-team@google.com>
  - fb4ea46062895cb9340166c9dcc61ec4467bd834 Avoid weak virtual table warnings (-Wweak-vtables) and re... by Abseil Team <absl-team@google.com>

GitOrigin-RevId: 989557e6b443a81b5ad9bd0d0c704edbe96c09c9
Change-Id: I6b8119c3f16e9d0cb9b5fd6e750502c9dad8e257