Improve ElementsAreArray mismatch explanations for readability #4934

[ShrutiPundir17]

Fixes #4934

Summary

This change improves failure diagnostics for ElementsAre* and UnorderedElementsAre* matchers by making explanations more structured and easier to scan during debugging loops.

What changed

• Updated ElementsAreMatcherImpl mismatch explanations to be more explicit:
  • size mismatch now reports:
    • expected size
    • actual size
  • element mismatch now reports:
    • mismatch index
    • actual value
    • expected matcher description
    • detail line from matcher negation/explanation
• Updated successful non-trivial match explanation wording to a cleaner element #N matches: ... form.
• Updated unordered matcher explanations to consistently use Expected vs Actual terminology:
  • unmatched expected entries are listed as Expected #...
  • unmatched actual entries are listed as Actual #...
  • pairing diagnostics now print as Actual #X <-> Expected #Y
• Updated affected expectation strings in container matcher tests accordingly.

Why

Current output for (Unordered)ElementsAreArray failures can be difficult to parse quickly, especially with large struct payloads.
This change prioritizes:

• faster visual diffing
• consistent LHS/RHS terminology
• clearer first-line diagnosis before details

Scope

Only diagnostic message formatting and corresponding tests were changed.
Matching semantics and matcher algorithms are unchanged.

Files touched

• googlemock/include/gmock/gmock-matchers.h
• googlemock/src/gmock-matchers.cc
• googlemock/test/gmock-matchers-containers_test.cc

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