Split Help.styleItemDescription into option/subcommand/argument

[shadowspawn]

Problem

I noticed the inconsistency when documenting the routines in #2282.

Have option+subcommand+argument flavours for stringify but not for style. If someone wanted the description colours to match the term colours they would be out of luck. I don't think many people will want separate styles, but easy to make the separation right from the start.

	stringify(object)	style(string)	default style
4	argumentTerm	styleArgumentTerm	styleArgumentText
5	argumentDescription	styleItemDescription	styleDescriptionText
6	optionTerm	styleOptionTerm	styleOptionText
7	optionDescription	styleItemDescription	styleDescriptionText
8	subcommandTerm	styleSubcommandTerm	b, c, d
9	subcommandDescription	styleItemDescription	styleDescriptionText

Solution

Split style for item descriptions into fine-grained option+subcommand+argument. Consistent pattern.