[LANG-1656] Add Supplier-based variants of firstNonBlank and firstNonEmpty for short-circuit evaluation

[aidanow-uni]

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Description of Issue
The PR addresses the JIRA issue titled 'Short-circuit operation of firstNonBlank and firstNonEmpty', a minor feature request originally proposed by Zhengkai Wang.

The existing methods firstNonBlank and firstNonEmpty in StringUtils.java evaluate all input strings immediately. This can lead to extra computational overhead when some arguments are expensive to compute, such as those involving remote API calls or database queries.

The feature request aims to introduce supplier-based variants of these methods, which support lazy evaluation and short-circuit behaviour.

Implementation
To resolve this, two new methods were added to StringUtils:

1. firstNonBlankSupplier(Supplier... suppliers)
   • Iterates through suppliers in order
   • Returns immediately once a non-blank supplier is found
2. firstNonEmptySupplier(Supplier... suppliers)
   • Similar to above, but checks for non-empty rather than non-blank strings.

Introducing new methods instead of modifying existing ones ensures backward compatibility with existing firstNonBlank and firstNonEmpty implementations. It avoids method overloading ambiguity and also creates a clear separation between eager and lazy variants.

Validation and Testing

1. Basic functionality tests
   • Implemented in StringUtilsEmptyBlankTest.
   • Methods testFirstNonBlankSupplier() and testFirstNonEmptySupplier() validate:
     • Correct return of the first non-blank/non-empty string.
     • Handling of null inputs, empty arrays, and suppliers that return blank or empty values.
2. Lazy evaluation tests
   • testFirstNonBlankSupplierLazyEvaluation() and testFirstNonEmptySupplierLazyEvaluation() verify short-circuit behavior using AtomicBoolean flags.
   • Confirms that once a valid result is found, subsequent suppliers are not invoked, ensuring performance efficiency.
3. Safety guarantees
   • All methods include null checks to prevent NullPointerException.
   • Edge cases covered in original tests are preserved.

[garydgregory]

Jira: https://issues.apache.org/jira/browse/LANG-1656

[garydgregory]

I don't see the need for such a utility. Can this even be reused in Lang? What's a use-case in another code base, like any other Commons component?