feat: introduce escoria-ui-keyboard-9verbs to verify register_custom_input_handler() API

This commit was started by copying `addons/escoria-ui-9verbs` as the
basis for `addons/escoria-ui-keyboard-9verbs`. It was then amended to
wire up keyboard shortcuts for each verb using the new
`register_custom_input_handler()` API.

Note that `addons/escoria-ui-keyboard-9verbs/input_map.gd` introduces
one action per verb and provides a `add_actions_to_input_map()`
function to add the actions to the `InputMap`. The `_process_input()`
function in `game.gd` is responsible for mapping each action to the
appropriate call to `verbs_menu.on_action_selected()`.

addons/escoria-ui-keyboard-9verbs/tooltip/action_target_tooltip.tscn

@@ -0,0 +1,14 @@
+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://addons/escoria-ui-keyboard-9verbs/tooltip/tooltip_action_target.gd" type="Script" id=1]
+
+[node name="tooltip" type="RichTextLabel"]
+anchor_right = 1.0
+anchor_bottom = 1.0
+bbcode_enabled = true
+bbcode_text = "[center][/center]"
+scroll_active = false
+script = ExtResource( 1 )
+__meta__ = {
+"_edit_use_anchors_": false
+}

addons/escoria-ui-keyboard-9verbs/tooltip/tooltip_action_target.gd

@@ -0,0 +1,31 @@
+extends ESCTooltip
+
+func update_tooltip_text():
+	bbcode_text = "[center]"
+	bbcode_text += "[color=#" + color.to_html(false) + "]"
+	if !current_action.empty():
+		bbcode_text += current_action + "\t"
+	bbcode_text += current_target
+
+	if waiting_for_target2 and current_target2.empty():
+		bbcode_text += "\t" + current_prep
+
+	if !current_target2.empty():
+		bbcode_text += "\t" + current_prep + "\t" + current_target2
+
+	bbcode_text += "[/color]"
+	bbcode_text += "[/center]"
+
+#	push_align(RichTextLabel.ALIGN_CENTER)
+#	if !current_action.empty():
+#		add_text(current_action + "\t")
+#
+#	add_text(current_target)
+#
+#	if waiting_for_target2 and current_target2.empty():
+#		add_text("\t" + current_prep)
+#
+#	if !current_target2.empty():
+#		add_text("\t" + current_prep + "\t" + current_target2)
+#
+#	pop()