For builtins that have the same name as common commands, it might not
be entirely obvious that there is another page.
So, for those builtins, we add a note, but only in the man pages.
(exception is true and false because the note would be longer than the
page, and it's fridging true and false)
Fixes#8077.
Instead of informing the bell character (hex 07), the example was using
an escaped \ followed by x07.
$ echo \\x07
\x07
$ echo \x07
$ echo \x07 | od -a
0000000 bel nl
0000002
$
* docs: Use \u instead of \\u
Instead of informing the Unicode character 慡, this example was using an
escaped \ followed by u6161.
$ echo \\u6161
\u6161
$ echo \u6161
慡
Before:
$ string escape --style=var 'a1 b2'\\u6161 | string unescape --style=var
a1 b2\u6161
Now:
$ string escape --style=var 'a1 b2'\u6161 | string unescape --style=var
a1 b2慡
