[12.x] fix: resolve PHP compatibility issues in HandleExceptions

[imhayatunnabi]

Issue

HandleExceptions bootstrap has PHP compatibility issues:

• get_exception_handler() and get_error_handler() only available in PHP 8.5+
• Static method using $this causing errors
• Version-specific enable() call with wrong arguments

Solution

• Replace get_*_handler() with set_*_handler(null) for PHP <8.5 compatibility
• Fix static context by using method_exists() check instead of $this
• Simplify enable() call to remove argument mismatch

Testing

• Maintains same functionality across PHP versions
• No breaking changes to existing behavior
• Backward compatible with PHP 7.4+

Changes

• flushHandlersState(): Use compatible handler detection
• ErrorHandler check: Use method existence validation
• Remove version-specific logic causing argument errors