feat(terminal): and stylebox support

Adds support for 'normal' and 'focus' Style Boxes to Terminal node.
Changes default background color to transparent, with background to be
set by StyleBox.

If background color is not transparent, will draw a background color
rect to cover the entire control over the top of any stylebox. This is
consistent with the behavior of the TextEdit node with regards to theme
colors and styleboxes.

test/visual_regression/background.tscn

@@ -0,0 +1,13 @@
+[gd_scene load_steps=2 format=3 uid="uid://bk450yhh0sx2f"]
+
+[ext_resource type="Texture2D" uid="uid://2em8p7vcmp33" path="res://docs/_static/images/icon.png" id="1_osuf4"]
+
+[node name="Background" type="TextureRect"]
+z_index = -1
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+texture = ExtResource("1_osuf4")
+stretch_mode = 1

test/visual_regression/test_visual_regression.gd

@@ -88,6 +88,8 @@ class TestVisualRegression:
 		assert_match("default_theme")
 
 	func test_transparency():
+		subject.add_child(preload("./background.tscn").instantiate())
+		subject.add_theme_stylebox_override("normal", StyleBoxEmpty.new())
 		subject.add_theme_color_override("foreground_color", Color(0, 1, 0, 0.5))
 		subject.add_theme_color_override("background_color", Color(1, 0, 0, 0.5))
 		subject.write("bg red, 50% transparency\r\n")
@@ -104,3 +106,39 @@ class TestVisualRegression:
 		subject.write("👈🤮👉💩👃😍🤥😤🙏🤟")
 		await wait_frames(30)
 		assert_match("emoji")
+
+	func test_solid_invert_selection():
+		subject.write("██████████\r\n██████████")
+		subject.add_theme_color_override("background_color", Color.ORANGE)
+		subject.inverse_mode = Terminal.INVERSE_MODE_INVERT
+		subject.select(0, 5, 1, 6)
+		await wait_frames(30)
+		assert_match("solid_invert_selection")
+
+	func test_solid_swap_selection():
+		subject.write("██████████\r\n██████████")
+		subject.add_theme_color_override("background_color", Color.ORANGE)
+		subject.inverse_mode = Terminal.INVERSE_MODE_SWAP
+		subject.select(0, 5, 1, 6)
+		await wait_frames(30)
+		assert_match("solid_swap_selection")
+
+	func test_transparent_invert_selection():
+		subject.add_child(preload("./background.tscn").instantiate())
+		subject.write("██████████\r\n██████████")
+		subject.add_theme_color_override("background_color", Color.TRANSPARENT)
+		subject.add_theme_stylebox_override("normal", StyleBoxEmpty.new())
+		subject.inverse_mode = Terminal.INVERSE_MODE_INVERT
+		subject.select(0, 5, 1, 6)
+		await wait_frames(30)
+		assert_match("transparent_invert_selection")
+
+	func test_transparent_swap_selection():
+		subject.add_child(preload("./background.tscn").instantiate())
+		subject.write("██████████\r\n██████████")
+		subject.add_theme_color_override("background_color", Color.TRANSPARENT)
+		subject.add_theme_stylebox_override("normal", StyleBoxEmpty.new())
+		subject.inverse_mode = Terminal.INVERSE_MODE_SWAP
+		subject.select(0, 5, 1, 6)
+		await wait_frames(30)
+		assert_match("transparent_swap_selection")