Refactor JVM instruction hierarchy and translation

Introduces abstract base classes for JVM instructions (e.g., arithmetic, branch, field access, constant load) in JvmInstructions.qll, and updates the IR translation logic to use these new abstractions. Renames and unifies temp variable tags for consistency. Simplifies and generalizes TranslatedElement and TranslatedInstruction logic to leverage the new class hierarchy, improving maintainability and extensibility of JVM bytecode modeling.

Author: gfs