Add TryGetOptionArgument

[SimonCropp]

So usages of TryGetOptionArgumentList are problematic

• some usages use the first arg and ignore the rest
• some usages check if there is only one and dont use the first if there is more than one
• some usages assume there is 1 and will throw if that is not correct

so this PR adds TryGetOptionArgument. which will formalize the usages. it will:

• return false if there is no arg
• return false if there is no items in the arg
• throw if there is more than 1