Fix case-insensitive semantics for LinkedCaseInsensitiveMap entrySet

[TerryTaoYY]

Summary

Align LinkedCaseInsensitiveMap’s entrySet() view with the map’s case-insensitive key contract by making entrySet().contains(..) and entrySet().remove(..) perform case-insensitive key resolution.

Background

LinkedCaseInsensitiveMap provides case-insensitive behavior for containsKey/get/remove. However, entrySet() operations previously delegated to the backing map’s entry set, which performs case-sensitive key comparisons. As a result, entry-based operations could miss existing mappings when callers used different key casing.

Example

LinkedCaseInsensitiveMap<String> map = new LinkedCaseInsensitiveMap<>();
map.put("Key", "value");

assertThat(map.containsKey("KEY")).isTrue();
assertThat(map.entrySet()).contains(Map.entry("KEY", "value")); // previously failed
assertThat(map.entrySet().remove(Map.entry("key", "value"))).isTrue();
assertThat(map).isEmpty();

Changes

• Implement case-insensitive key lookup for EntrySet.contains(Object) and EntrySet.remove(Object) via containsKey/get/remove
• Preserve Map.Entry semantics by requiring value equality (using ObjectUtils.nullSafeEquals) before removing

Tests

• ./gradlew :spring-core:test --tests org.springframework.util.LinkedCaseInsensitiveMapTests
• ./gradlew :spring-core:test