Disassembler: Add option to get register offsets

[Symbai]

For displacement and immediate we can get the offsets. For used registers we currently cannot. I'd like to request the possibility to retrieve the offsets for registers too (C#).

In my scenario I have an array of bytes where some registers are wildcarded. I need to know which register(s) was wildcarded from this array to deal with it later on.

namespace Iced.Intel {

	public readonly struct UsedRegister {

		public Register Register;
		public OpAccess Access;
++		public byte Offset;

	}
}

[wtfsck]

Register bits can be in multiple bytes, eg. one bit could be in the REX prefix and 3 other bits in the modrm byte, or the bits could be in different bytes in the VEX/EVEX/etc prefix. So there's no single byte offset that could be returned.

[Symbai]

And when the instruction has no prefix? I can change the proposed property to nullable byte so that it only returns the offset if its possible and null when its not, like in the cases you mentioned.

Edit: Here is an example of an instruction where a register is wildcarded: 48 8B ?? 30 => mov rsi,[r??+30]