Export of internal Abseil changes

--
47f13ea42ae272c995b1cd5073a45e046fa325eb by Matthew Brown <matthewbr@google.com>:

absl::StrFormat: Centralize FormatConversionCharSet vs FormatConversionSpec checking
 - Move it into a central location, rather than requiring individual overloads to
   validate.

PiperOrigin-RevId: 310583805

--
a567c8fc8032031d551d6b457755851f442e65ad by Gennadiy Rozental <rogeeff@google.com>:

Internal change

PiperOrigin-RevId: 310427635

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49848f7fab9b0f528d33f60cbccf688e2ea68afa by Gennadiy Rozental <rogeeff@google.com>:

Make Get/Set private methods of absl::Flag<T>.

PiperOrigin-RevId: 310413908
GitOrigin-RevId: 47f13ea42ae272c995b1cd5073a45e046fa325eb
Change-Id: I6530c754731c1a9463877561fa61786460ed60af

absl/flags/internal/parse.h

@@ -44,6 +44,13 @@ std::vector<char*> ParseCommandLineImpl(int argc, char* argv[],
                                         UsageFlagsAction usage_flag_act,
                                         OnUndefinedFlag on_undef_flag);
 
+// --------------------------------------------------------------------
+// Inspect original command line
+
+// Returns true if flag with specified name was either present on the original
+// command line or specified in flag file present on the original command line.
+bool WasPresentOnCommandLine(absl::string_view flag_name);
+
 }  // namespace flags_internal
 ABSL_NAMESPACE_END
 }  // namespace absl