Implement Pattern Matching for instanceof in AnnotationWriter

[alidandach]

This enhancement leverages Java 16's pattern matching for instanceof to streamline and improve the readability of type checking and casting within the annotation processing method. By replacing explicit casting after instanceof checks with pattern variables, the code becomes more concise, readable, and less prone to errors.

Key Changes:

• Utilize pattern matching for instanceof to eliminate the need for manual casting of array types (e.g., byte[], boolean[], short[], char[], int[], long[], float[], double[]).
• Enhance code maintainability and readability by reducing boilerplate and leveraging Java's type inference within control flow blocks.
• Ensure backward compatibility by maintaining the logic and functionality of the annotation processing while adopting modern language features for better code quality.

This update not only adopts the latest Java language features for better development practices but also sets a precedent for future code enhancements and refactoring efforts, promoting a more modern and efficient coding style within the project.

[snicoll]

@alidandach going forward, please refrain from submitting PRs that are about stylistic changes as I've shared already with you we prefer to do those ourselves. The class you've changed is part of ASM, and the following is our policy on such classes.

Please refrain from modifying classes under org.springframework.asm, org.springframework.cglib, and org.springframework.objenesis. Those include repackaged forks of the third-party libraries ASM, CGLIB, and Objenesis. Any refactoring to those classes should take place upstream in the originating repository. The Spring Framework will then pick up the changes when syncing with official updates of the forked third-party libraries.