test: Add descriptions to multiwidth test fixtures

tests/cmd/stdin-failure-multiwidth.stdin

@@ -1,5 +1,34 @@
+---
+Korean character (NFC)
+Grapheme clusters: 1, codepoints: 1, UnicodeWidthStr::width() == 2
+
 한 Apropriate world
+   ^^^^^^^^^^ highlight here
+
+---
+Korean character (NFD).
+Grapheme clusters: 1, codepoints: 3, UnicodeWidthStr::width() == 2
+
 한 Apropriate world
-😵‍💫 Apropriate world
+   ^^^^^^^^^^ highlight here
+
+---
+Eye in Speech Bubble Emoji (U+1F441 U+FE0F U+200D U+1F5E8 U+FE0F, Recommended Emoji ZWJ Sequences, v2.0)
+Grapheme clusters: 1, codepoints: 5, UnicodeWidthStr::width() == 2 (Read NOTE: https://github.com/unicode-rs/unicode-width)
+
 👁️‍🗨️ Apropriate world
+   ^^^^^^^^^^ highlight here
+
+---
+Face with spiral eyes (U+1F635 U+200D U+1F4AB, Recommended Emoji ZWJ Sequence, v13.1)
+Grapheme clusters: 1, codepoints: 3, UnicodeWidthStr::width() == 4 (Read NOTE: https://github.com/unicode-rs/unicode-width)
+
+😵‍💫 Apropriate world
+     ^^^^^^^^^^ highlight here
+
+---
+Horizontal tab (\t, U+09)
+Grapheme clusters: 1, codepoints: 1, UnicodeWidthStr::width() == 0
+
 	Apropriate world
+^^^^^^^^^^ highlight here

tests/cmd/stdin-failure-multiwidth.stdout

@@ -1,30 +1,30 @@
 error: `Apropriate` should be `Appropriate`
-  --> -:1:2
+  --> -:5:2
   |
-1 | 한 Apropriate world
+5 | 한 Apropriate world
   |    ^^^^^^^^^^
   |
 error: `Apropriate` should be `Appropriate`
-  --> -:2:2
+  --> -:12:2
    |
-2 | 한 Apropriate world
+12 | 한 Apropriate world
    |    ^^^^^^^^^^
    |
 error: `Apropriate` should be `Appropriate`
-  --> -:3:2
+  --> -:19:2
    |
-3 | 😵‍💫 Apropriate world
+19 | 👁️‍🗨️ Apropriate world
    |    ^^^^^^^^^^
    |
 error: `Apropriate` should be `Appropriate`
-  --> -:4:2
+  --> -:26:2
    |
-4 | 👁️‍🗨️ Apropriate world
+26 | 😵‍💫 Apropriate world
    |      ^^^^^^^^^^
    |
 error: `Apropriate` should be `Appropriate`
-  --> -:5:1
+  --> -:33:1
    |
-5 |  Apropriate world
+33 |  Apropriate world
    | ^^^^^^^^^^
    |