MINIFICPP-1398 Add strftime-based fallback to EL :format() when the date.h library is not available

[szaszm]

• Implement fallback expr_format for the UTC/GMT and localtime cases based on strftime/std::put_time
• Make the current behavior of unsetting EXPRESSION_LANGUAGE_USE_DATE on windows explicit
• Move existing tests covering cases implemented in the fallback outside of the #ifdef guard
• Enable :format() and :toDate() regardless of EXPRESSION_LANGUAGE_USE_DATE

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