Eliminate shadowed variable warnings on intel

[gsjaardema]

The intel-19 compiler warns about hidden variables:

/s/dev/nightly/libraries/ioss/src/fmt/format.h(2689): warning #1599: declaration hides variable "begin" (declared at line 2668)
      FMT_CONSTEXPR void operator()(const Char* begin, const Char* end) {
                                                ^
          detected during:
            instantiation of "Context::iterator fmt::v7::vformat_to<ArgFormatter,Char,Context>(ArgFormatter::iterator, fmt::v7::basic_string_view<Char>, fmt::v7::basic_format_args<Context>, fmt::v7::detail::locale_ref) [with ArgFormatter=fmt::v7::detail::arg_formatter<fmt::v7::detail::buffer_appender<char>, char>, Char=char, Context=fmt::v7::format_context]" at line 3492
            instantiation of "fmt::v7::detail::buffer_appender<Char> fmt::v7::detail::vformat_to(fmt::v7::detail::buffer<Char> &, fmt::v7::basic_string_view<Char>, fmt::v7::basic_format_args<fmt::v7::basic_format_context<fmt::v7::detail::buffer_appender<fmt::v7::type_identity_t<Char>>, fmt::v7::type_identity_t<Char>>>) [with Char=char]" at line 1413 of "/s/dev/nightly/libraries/ioss/src/fmt/format-inl.h"

/s/dev/nightly/libraries/ioss/src/fmt/format.h(2689): warning #1599: declaration hides variable "end" (declared at line 2669)
      FMT_CONSTEXPR void operator()(const Char* begin, const Char* end) {
                                                                   ^
          detected during:
            instantiation of "Context::iterator fmt::v7::vformat_to<ArgFormatter,Char,Context>(ArgFormatter::iterator, fmt::v7::basic_string_view<Char>, fmt::v7::basic_format_args<Context>, fmt::v7::detail::locale_ref) [with ArgFormatter=fmt::v7::detail::arg_formatter<fmt::v7::detail::buffer_appender<char>, char>, Char=char, Context=fmt::v7::format_context]" at line 3492
            instantiation of "fmt::v7::detail::buffer_appender<Char> fmt::v7::detail::vformat_to(fmt::v7::detail::buffer<Char> &, fmt::v7::basic_string_view<Char>, fmt::v7::basic_format_args<fmt::v7::basic_format_context<fmt::v7::detail::buffer_appender<fmt::v7::type_identity_t<Char>>, fmt::v7::type_identity_t<Char>>>) [with Char=char]" at line 1413 of "/s/dev/nightly/libraries/ioss/src/fmt/format-inl.h"

Rename the second set of variables to pbegin and pend to eliminate warning.

I agree that my contributions are licensed under the {fmt} license, and agree to future changes to the licensing.