Changes imported from Abseil "staging" branch:

  - 432508bf64998983b3c194d5f164872ce3c2e573 Put visibility tags into absl external build files by Jon Cohen <cohenjon@google.com>
  - 25d59d11e7b833fe632cddb5bf4d76075ae6282b Use ABSL_PREDICT_TRUE instead of *FALSE for the range che... by Jon Cohen <cohenjon@google.com>
  - 8d8a5890a55ddd19aac849748441eeb57c684f10 Better detection for MSVC support on std::optional. by Xiaoyi Zhang <zhangxy@google.com>
  - c1b31e4a97939885c3bbc23ecb093e9619e73ad1 Internal cleanup by Gennadiy Rozental <rogeeff@google.com>
  - 4f56ad20c4eeccc6f5fb21ec6c7191233d34a090 Internal change. by Matt Calabrese <calabrese@google.com>
  - d2a02b52c75c295708170f4d17b7ff442c8d6a97 Fixed a minor typo in the SimpleAtob() function comment. by Abseil Team <absl-team@google.com>
  - 5adbff5c23a45278d06de2ef3a29ea51b0d1269e Internal cleanup by Gennadiy Rozental <rogeeff@google.com>

GitOrigin-RevId: 432508bf64998983b3c194d5f164872ce3c2e573
Change-Id: I32ddd151d3350b96a22e8f1830f19b59374953ad