block: Use RichTextLabel for tooltip

By default, a plain-text label is used which does not support rich text
formatting.

Define a `Tooltip` scene; and override `Control._make_custom_tooltip()` in `Block` to
return an instance of this scene.

`Tooltip` is initially just a `RichTextLabel` with BBCode enabled and a custom
minimum size set as suggested by the `_make_custom_tooltip()` documentation:

> Note: The tooltip is shrunk to minimal size. If you want to ensure it's fully
> visible, you might want to set its `custom_minimum_size` to some non-zero
> value.

We override the theme styles on the `RichTextLabel` to match the styles used in
the built-in inspector's help tooltips. In particular, bold, italic and
bold-italic text doesn't work without overriding these styles. The [BBCode in
RichTextLabel][0] documentation claims:

> If no custom bold or italic fonts are defined, faux bold and italic fonts
> will be generated by Godot.

but empirically this is not true.

The Editor Theme Explorer plugin
<https://github.com/YuriSizov/godot-editor-theme-explorer> was useful, as was
reading the editor source code, specifically `editor_fonts.cpp` and
`editor_help.cpp`.

None of the existing `tooltip_text` properties in the codebase use the `[`
character that is used by BBCode tags, so there is no need to adjust the
existing tooltips to keep displaying as they previously did.

https://phabricator.endlessm.com/T35540

[0]: https://docs.godotengine.org/en/stable/tutorials/ui/bbcode_in_richtextlabel.html#reference

Author: wjt

addons/block_code/ui/blocks/block/block.gd

@@ -74,3 +74,8 @@ func serialize_props(prop_names: Array) -> Array:
 	for p in prop_names:
 		pairs.append([p, self.get(p)])
 	return pairs
+
+func _make_custom_tooltip(for_text) -> Control:
+	var tooltip = preload("res://addons/block_code/ui/tooltip/tooltip.tscn").instantiate()
+	tooltip.text = for_text
+	return tooltip

addons/block_code/ui/tooltip/tooltip.gd

@@ -0,0 +1,22 @@
+@tool
+class_name Tooltip
+extends RichTextLabel
+## Rich-text control for block tooltips that matches the built-in inspector's tooltips' font styles
+
+func override_font(font_name: StringName, editor_font_name: StringName) -> Font:
+	var font = get_theme_font(editor_font_name, &"EditorFonts")
+	add_theme_font_override(font_name, font)
+	return font
+
+func _ready():
+	# Set fonts to match documentation tooltips in inspector
+	override_font(&"normal_font", &"doc")
+	override_font(&"mono_font", &"doc_source")
+	override_font(&"bold_font", &"doc_bold")
+	var italics = override_font(&"italics_font", &"doc_italic")
+
+	# No doc_ style for bold italic; fake it by emboldening the italic style
+	var bold_italics = FontVariation.new()
+	bold_italics.set_base_font(italics)
+	bold_italics.set_variation_embolden(1.2)
+	add_theme_font_override(&"bold_italics_font", bold_italics)

addons/block_code/ui/tooltip/tooltip.tscn

@@ -0,0 +1,14 @@
+[gd_scene load_steps=2 format=3 uid="uid://bmxco03vqyq2t"]
+
+[ext_resource type="Script" path="res://addons/block_code/ui/tooltip/tooltip.gd" id="1_4ko6a"]
+
+[node name="Tooltip" type="RichTextLabel"]
+custom_minimum_size = Vector2(360, 48)
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+bbcode_enabled = true
+fit_content = true
+script = ExtResource("1_4ko6a")