[jay-2611]

Fixes #4934

Summary

Improves failure diagnostics for ElementsAre matchers when element values or struct fields fail to match.

Problem

Previously, mismatch explanations for ElementsAre printed actual and expected values in a single dense paragraph:
whose element #1 (ActualVal) isn't equal to ExpectedVal

For complex structures or large arrays, this required manual editing and visual scanning to isolate mismatched fields.

Solution

Formats the mismatch explanation with clear, structured LHS/RHS lines:

element mismatch at index 1:
  Actual   #1: <actual_value>
  Expected #1: <expected_matcher_description>
  Detail: <optional_explanation>