Implement instruction: ADDX

[tjhancocks]

Feature Request
An implementation for the ADDX instruction needs to be added to the emulation layer. Below is a brief description of the ADDX instruction taken from the M68000 Programmers Reference Manual.

Adds the source operand and the extend bit to the destination operand and stores the result in the destination location. The operands can be addressed in two different ways:

1. Data register to data register—The data registers specified in the instruction contain the operands.
2. Memory to memory—The address registers specified in the instruction address the operands using the predecrement addressing mode.
   The size of the operation can be specified as byte, word, or long.

Describe the solution you'd like
The solution should match the existing conventions and patterns used by other implemented instructions. At the time of reporting this only includes the ABCD instruction.

Describe alternatives you've considered
N/a

Additional context
N/a