RFR: 8373661: Add edge case tests for Objects.requireNonNull methods [v4]

[eunbin son]

> ## Summary
> Adds comprehensive edge case tests for `Objects.requireNonNull`, 
> `requireNonNullElse`, and `requireNonNullElseGet` methods to improve 
> test coverage.
> 
> ## Problem
> The current test suite for `Objects.requireNonNull` methods covers 
> basic cases but lacks edge case coverage.
> 
> ## Solution
> This PR adds tests for the following edge cases:
> - requireNonNull with null Supplier parameter
> - requireNonNull with Supplier that throws exception
> - requireNonNullElse with both arguments null
> - requireNonNullElseGet with null supplier
> - requireNonNullElseGet with supplier returning null
> 
> ## Issue
> Fixes JDK-8373661
> 
> **JBS Issue Link**: https://bugs.java.com/bugdatabase/view_bug?bug_id=JDK-8373661
> 
> ## Type of Change
> - [x] Test addition/modification
> - [ ] Bug fix
> - [ ] New feature
> - [ ] Documentation improvement
> - [ ] Refactoring
> 
> ## Testing
> 
> make test TEST="jtreg:test/jdk/java/util/Objects"

eunbin son has updated the pull request incrementally with one additional commit since the last revision:

  8373661: Use assertSame for exception instance verification
  
  Updated testRequireNonNullWithSupplierThrowingException to allocate
  the exception outside of the lambda and use assertSame to verify
  the same exception instance is thrown, as suggested by @liach.
  
  This provides a more precise verification that the exception from
  the supplier is thrown directly, not wrapped.
  
  Thanks to @liach for the feedback.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28845/files
  - new: https://git.openjdk.org/jdk/pull/28845/files/03017eff..3986ed4b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28845&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28845&range=02-03

  Stats: 6 lines in 1 file changed: 1 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/28845.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28845/head:pull/28845

PR: https://git.openjdk.org/jdk/pull/28845