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/asciicast/asciicast.tscn

@@ -1,19 +1,26 @@
-[gd_scene load_steps=3 format=2]
+[gd_scene load_steps=4 format=3 uid="uid://did1ipako11pd"]
 
-[ext_resource path="res://addons/godot_xterm/terminal.gd" type="Script" id=1]
-[ext_resource path="res://examples/asciicast/example.cast" type="Animation" id=6]
+[ext_resource type="Theme" uid="uid://b7vd50tw2g1nl" path="res://themes/default.tres" id="1_nsh8i"]
+[ext_resource type="Animation" uid="uid://dcgqvylq0648u" path="res://examples/asciicast/example.cast" id="2_3048a"]
 
-[node name="Terminal" type="Control"]
+[sub_resource type="AnimationLibrary" id="AnimationLibrary_02l7k"]
+_data = {
+"example": ExtResource("2_3048a")
+}
+
+[node name="Terminal" type="Terminal"]
+anchors_preset = 15
 anchor_right = 1.0
 anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
 focus_mode = 1
-script = ExtResource( 1 )
-__meta__ = {
-"_edit_use_anchors_": false
-}
+theme = ExtResource("1_nsh8i")
 
 [node name="AnimationPlayer" type="AnimationPlayer" parent="."]
 autoplay = "example"
 playback_speed = 2.0
 method_call_mode = 1
-anims/example = ExtResource( 6 )
+libraries = {
+"": SubResource("AnimationLibrary_02l7k")
+}