Show Japanese text and close the gap in the top bar

Godot's built-in font has no Japanese, so kanji in song names showed as
boxes. The theme now sets Godot's own Open Sans SemiBold as its default
font, with Noto Sans JP Medium as fallback. The Noto file's line metrics
are set to Open Sans's, so line heights stay the same and every other
screen is pixel-identical; fonts/README.md explains how to redo it.

Search and Sync move right to where the Statistics button was.

tests/integration/test_theme.gd

@@ -119,3 +119,19 @@ func test_main_window_background_comes_from_the_theme_and_lets_clicks_through()
 	assert_int(background.mouse_filter).is_equal(Control.MOUSE_FILTER_IGNORE)
 	assert_float(background.anchor_right).is_equal(1.0)
 	assert_float(background.anchor_bottom).is_equal(1.0)
+
+
+func test_default_font_shows_japanese() -> void:
+	var font: Font = _theme.default_font
+	for character: String in "幕開けミッション":
+		var found: bool = font.fallbacks.any(
+				func(fallback: Font) -> bool: return fallback.has_char(character.unicode_at(0)))
+		assert_bool(found).override_failure_message("No font has " + character).is_true()
+
+
+func test_japanese_fallback_keeps_the_line_height_of_godots_font() -> void:
+	var builtin: Font = ThemeDB.get_default_theme().default_font
+	for size: int in [16, 18, 20, 25, 35, 50]:
+		assert_float(_theme.default_font.get_height(size)) \
+				.override_failure_message("Line height at size %d" % size) \
+				.is_equal(builtin.get_height(size))