docs(builtin): fix and annotate language blocks (#24506)

scripts/gen_eval_files.lua

@@ -217,14 +217,14 @@ local CONFIG = {
       'same way.  The difference is that a String is handled like it is one line.',
       'When it contains a "\\n" character, this is not seen as a line break for the',
       'pattern.  It can be matched with a "\\n" in the pattern, or with ".".  Example:',
-      '>',
-      '\t:let a = "aaaa\\nxxxx"',
-      '\t:echo matchstr(a, "..\\n..")',
-      '\taa',
-      '\txx',
-      '\t:echo matchstr(a, "a.x")',
-      '\ta',
-      '\tx',
+      '>vim',
+      '\tlet a = "aaaa\\nxxxx"',
+      '\techo matchstr(a, "..\\n..")',
+      '\t" aa',
+      '\t" xx',
+      '\techo matchstr(a, "a.x")',
+      '\t" a',
+      '\t" x',
       '',
       'Don\'t forget that "^" will only match at the first character of the String and',
       '"$" at the last character of the string.  They don\'t match after or before a',