gui2/tslider: Add minimal variant without a text label

The default variant's text label is both inflexible in content (can't
customize the format for non-edge values) and layout (reserves way more
space than it needs at a time for its text label, often resulting in
huge horizontal gaps between a slider and an adjacent widget). This
makes it unsuitable for use in gui2::tchat_log.

This new minimal variant will be wired into gui2::tchat_log next.

data/gui/default/widget/slider_minimal.cfg

@@ -0,0 +1,100 @@
+#textdomain wesnoth-lib
+###
+### Experimental slider variant that does not have a text label since the
+### default variant does have one that takes up more space than is strictly
+### necessary and I (shadowm) can't deal with all the magic numbers in it.
+###
+
+#define _GUI_STATE IMAGE_SUFFIX GROOVE_COLOR
+	[draw]
+
+		#
+		# Groove
+		#
+
+		[line]
+			x1 = 0
+			y1 = "(height / 2)"
+			x2 = "(width - 1)"
+			y2 = "(height / 2)"
+
+			color = {GROOVE_COLOR}
+			thickness = 1
+		[/line]
+
+		#
+		# Slider
+		#
+
+		[image]
+			x = "(positioner_offset)"
+			y = "(if (image_height < height, (height - image_height) / 2, 0))"
+			name = "buttons/sliders/slider{IMAGE_SUFFIX}"
+		[/image]
+
+	[/draw]
+#enddef
+
+#define _GUI_RESOLUTION RESOLUTION MIN_WIDTH DEFAULT_WIDTH HEIGHT POSITIONER_LENGTH
+
+	[resolution]
+
+		{RESOLUTION}
+
+		min_width = {MIN_WIDTH}
+		min_height = {HEIGHT}
+
+		default_width = {DEFAULT_WIDTH}
+		default_height = {HEIGHT}
+
+		max_width = 0
+		max_height = {HEIGHT}
+
+		minimum_positioner_length = {POSITIONER_LENGTH}
+		maximum_positioner_length = {POSITIONER_LENGTH}
+
+		#text_font_size = 1 # placeholder
+
+		[state_enabled]
+			{_GUI_STATE
+				".png"
+				({GUI__FONT_COLOR_ENABLED__DEFAULT})
+			}
+		[/state_enabled]
+
+		[state_disabled]
+			{_GUI_STATE
+				".png~GS()"
+				({GUI__FONT_COLOR_DISABLED__DEFAULT})
+			}
+		[/state_disabled]
+
+		[state_pressed]
+			{_GUI_STATE
+				"-pressed.png"
+				({GUI__FONT_COLOR_ENABLED__DEFAULT})
+			}
+		[/state_pressed]
+
+		[state_focussed]
+			{_GUI_STATE
+				"-active.png"
+				({GUI__FONT_COLOR_ENABLED__DEFAULT})
+			}
+		[/state_focussed]
+
+	[/resolution]
+#enddef
+
+[slider_definition]
+	id = "minimal"
+	description = "A slider without a value label."
+
+	# Tiny gui sizes haven't been tested yet so might need some tuning.
+	{_GUI_RESOLUTION ({GUI_TINY__RESOLUTION})  75 125 11  8 }
+	{_GUI_RESOLUTION ()                       150 250 22 16 }
+
+[/slider_definition]
+
+#undef _GUI_STATE
+#undef _GUI_RESOLUTION