encoding.utf8.east_asian: add support for East_Asian_Width (#8978)

See https://www.unicode.org/reports/tr11/

vlib/encoding/utf8/east_asian/east_asian_width_test.v

@@ -0,0 +1,23 @@
+module east_asian
+
+fn test_width() {
+	assert east_asian_width_property_at('A', 0) == .narrow
+	assert east_asian_width_property_at('Ａ', 0) == .full
+	assert east_asian_width_property_at('ｱ', 0) == .half
+	assert east_asian_width_property_at('ア', 0) == .wide
+	assert east_asian_width_property_at('☆', 0) == .ambiguous
+	assert east_asian_width_property_at('ج', 0) == .neutral
+	assert display_width('abc', 1) == 3
+	assert display_width('ひらがな', 1) == 8
+	assert display_width('カタカナ', 1) == 8
+	assert display_width('ｶﾀｶﾅ', 1) == 4
+	assert display_width('한글', 1) == 4
+	assert display_width('한자', 1) == 4
+	assert display_width('漢字', 1) == 4
+	assert display_width('简体字', 1) == 6
+	assert display_width('繁體字', 1) == 6
+	assert display_width('अरबी लिपि', 1) == 9
+	assert display_width('☆', 1) == 1
+	assert display_width('☆', 2) == 2
+	assert display_width('🐈👽📛', 1) == 6
+}