Export of internal Abseil changes.

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92e1bd6dc9e64163659028b640427d6d8573e41c by Abseil Team <absl-team@google.com>:

Don't enable ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE with MSVC when used with nvcc.

With nvcc on Windows __has_trivial_assign(int) is false; that leads to a failure of the check in is_trivially_copy_assignable. A better solution would probably be to use the std-provided check in this case, but that seems like a more intrusive change.

PiperOrigin-RevId: 236135209

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26cee4a7e647076b4e2f88375b4848d1469e55ed by Derek Mauro <dmauro@google.com>:

Remove hashtablez_force_sampling from the open-source release.
This should not have been released. It is internal-only and not portable.

Fixes https://github.com/abseil/abseil-cpp/issues/268

PiperOrigin-RevId: 235978666

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935a885ec0e108963014f1bb79f00102da8f3871 by CJ Johnson <johnsoncj@google.com>:

Internal change

PiperOrigin-RevId: 235976027

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1c148c89de6064031f1ad9f2eeac0331bd77b7b0 by Tom Manshreck <shreck@google.com>:

Add design note for absl::from_chars to abseil.io

Fixes #165

PiperOrigin-RevId: 235975923
GitOrigin-RevId: 92e1bd6dc9e64163659028b640427d6d8573e41c
Change-Id: I220b0bbb46742070ea8c2a94b06007ecae76fe0f