Move away from [+tag] macros

[soliton-]

Describe the desired feature

It'd be good to move away from macros of the form:

wesnoth/data/core/macros/unit-utils.cfg

Lines 180 to 185 in 0222fda

	#define GUARDIAN
	# Meant to be used as a suffix to a unit-generating macro call.
	[+unit]
	ai_special=guardian
	[/unit]
	#enddef

which are most commonly used following unit creation macro calls. I think it's a bad habit especially in core macros.

We should either use a macro tailored for the use case that includes the additional parts or use a generic macro that allows adding whatever WML when calling the macro as in the case of the UNIT macro for example.

wesnoth/data/core/macros/unit-utils.cfg

Lines 22 to 32 in 0222fda

	#define UNIT SIDE TYPE X Y WML
	# Place a unit with embedded WML specified.
	#
	[unit]
	side={SIDE}
	type={TYPE}
	x={X}
	y={Y}
	{WML}
	[/unit]
	#enddef

When calling that macro the WML parameter there could be ai_special=guardian for example which completely avoids the need for the first macro.

I think one simple step would be to add an optional WML parameter to all core macros that would benefit from it or at least those that are currently used with [+tag] macros following them (for example LOYAL_UNIT). And then remove all instances of [+tag] macro calls following these macros and put the respective WML in that macro call instead.

For example {LOYAL_UNIT 1 Spearman 1 1} followed by {GUARDIAN} would become {LOYAL_UNIT 1 Spearman 1 1 (ai_special=guardian)}.

The obsolete [+tag] macros can then be deprecated indefinitely.

(See #7883 for one such macro example. That issue is mixed with using different defaults for unit macros though.)

[CelticMinstrel]

With the advent of optional macro parameters, I wonder if perhaps it's a good idea to consolidate all the unit macros into a single macro for placing a unit… though I think this still isn't quite possible. I don't know of any way to have an optional parameter that makes the unit loyal if present, for example. We'd probably need something like #ifarg?