Further progress towards Godot 4.0 support

- Primary example scenes (menu, terminal, and asciicast) working but
  still a lot of warning/error messages and some regressions.
- Editor integrated terminal works, but still a lot of warning/error
  messages and some regressions.
- Added support for "blink" display attribute.
- Removed GDScript terminal code. Terminal node is now purely a
  GDExtension. So is LibuvUtils.
- GUT tests not working yet.
- Still a lot of things to fix.
- So far, only built for and manually tested on Linux x86_64.

examples/retro_term/retro_term.tscn

@@ -1,9 +1,9 @@
-[gd_scene load_steps=6 format=2]
+[gd_scene load_steps=6 format=3 uid="uid://ddebdj001o1m5"]
 
-[ext_resource path="res://examples/menu/menu.tscn" type="PackedScene" id=1]
-[ext_resource path="res://themes/retro_green.tres" type="Theme" id=2]
+[ext_resource type="PackedScene" uid="uid://brjrtf5fpptw8" path="res://examples/menu/menu.tscn" id="1"]
+[ext_resource type="Theme" uid="uid://blh56m1gdieyu" path="res://themes/retro_green.tres" id="2"]
 
-[sub_resource type="Shader" id=1]
+[sub_resource type="Shader" id="1"]
 code = "/*
 Shader from Godot Shaders - the free shader library.
 godotshaders.com/shader/VHS-and-CRT-monitor-effect
@@ -234,31 +234,31 @@ void fragment()
 	COLOR = text;
 }"
 
-[sub_resource type="ShaderMaterial" id=2]
-shader = SubResource( 1 )
-shader_param/overlay = true
-shader_param/scanlines_opacity = 0.4
-shader_param/scanlines_width = 0.25
-shader_param/grille_opacity = 0.3
-shader_param/resolution = Vector2( 768, 240 )
-shader_param/pixelate = false
-shader_param/roll = true
-shader_param/roll_speed = 8.0
-shader_param/roll_size = 15.0
-shader_param/roll_variation = 1.8
-shader_param/distort_intensity = 0.05
-shader_param/noise_opacity = 0.4
-shader_param/noise_speed = 5.0
-shader_param/static_noise_intensity = 0.06
-shader_param/aberration = 0.0
-shader_param/brightness = 2.5
-shader_param/discolor = true
-shader_param/warp_amount = 1.0
-shader_param/clip_warp = false
-shader_param/vignette_intensity = 0.4
-shader_param/vignette_opacity = 0.5
+[sub_resource type="ShaderMaterial" id="2"]
+shader = SubResource("1")
+shader_parameter/overlay = true
+shader_parameter/scanlines_opacity = 0.4
+shader_parameter/scanlines_width = 0.25
+shader_parameter/grille_opacity = 0.3
+shader_parameter/resolution = Vector2(768, 240)
+shader_parameter/pixelate = false
+shader_parameter/roll = true
+shader_parameter/roll_speed = 8.0
+shader_parameter/roll_size = 15.0
+shader_parameter/roll_variation = 1.8
+shader_parameter/distort_intensity = 0.05
+shader_parameter/noise_opacity = 0.4
+shader_parameter/noise_speed = 5.0
+shader_parameter/static_noise_intensity = 0.06
+shader_parameter/aberration = 0.0
+shader_parameter/brightness = 2.5
+shader_parameter/discolor = true
+shader_parameter/warp_amount = 1.0
+shader_parameter/clip_warp = false
+shader_parameter/vignette_intensity = 0.4
+shader_parameter/vignette_opacity = 0.5
 
-[sub_resource type="Environment" id=3]
+[sub_resource type="Environment" id="3"]
 background_mode = 4
 glow_enabled = true
 glow_intensity = 1.0
@@ -266,36 +266,39 @@ glow_strength = 1.15
 glow_blend_mode = 0
 
 [node name="RetroTerm" type="Control"]
+layout_mode = 3
+anchors_preset = 15
 anchor_right = 1.0
 anchor_bottom = 1.0
-theme = ExtResource( 2 )
-__meta__ = {
-"_edit_use_anchors_": false
-}
+grow_horizontal = 2
+grow_vertical = 2
+theme = ExtResource("2")
 
 [node name="ColorRect" type="ColorRect" parent="."]
 show_behind_parent = true
+layout_mode = 1
+anchors_preset = 15
 anchor_right = 1.0
 anchor_bottom = 1.0
-color = Color( 0.156863, 0.156863, 0.156863, 1 )
-__meta__ = {
-"_edit_use_anchors_": false
-}
+grow_horizontal = 2
+grow_vertical = 2
+color = Color(0.156863, 0.156863, 0.156863, 1)
 
-[node name="Menu" parent="." instance=ExtResource( 1 )]
+[node name="Menu" parent="." instance=ExtResource("1")]
+layout_mode = 1
 offset_left = 30.0
 offset_top = 30.0
 
 [node name="CanvasLayer" type="CanvasLayer" parent="."]
 
 [node name="ColorRect" type="ColorRect" parent="CanvasLayer"]
-modulate = Color( 0, 1, 0.4, 1 )
-material = SubResource( 2 )
+modulate = Color(0, 1, 0.4, 1)
+material = SubResource("2")
+anchors_preset = 15
 anchor_right = 1.0
 anchor_bottom = 1.0
-__meta__ = {
-"_edit_use_anchors_": false
-}
+grow_horizontal = 2
+grow_vertical = 2
 
 [node name="WorldEnvironment" type="WorldEnvironment" parent="."]
-environment = SubResource( 3 )
+environment = SubResource("3")