basic/escape: allow truncation mode where "…" is always appended

So far we would append "…" or "..." when the string was wider than the specified
output width. But let's add a mode where the caller knows that the string being
passed is already truncated.

The condition for jumping back in utf8_escape_non_printable_full() was
off-by-one. But we only jumped to that label after doing a check with a
stronger condition, so I think it didn't matter. Now it matters because we'd
output the forced ellipsis one column too early.

src/basic/utf8.h

@@ -25,9 +25,9 @@ bool utf8_is_printable_newline(const char* str, size_t length, bool allow_newlin
 #define utf8_is_printable(str, length) utf8_is_printable_newline(str, length, true)
 
 char *utf8_escape_invalid(const char *s);
-char *utf8_escape_non_printable_full(const char *str, size_t console_width);
+char *utf8_escape_non_printable_full(const char *str, size_t console_width, bool force_ellipsis);
 static inline char *utf8_escape_non_printable(const char *str) {
-        return utf8_escape_non_printable_full(str, SIZE_MAX);
+        return utf8_escape_non_printable_full(str, SIZE_MAX, false);
 }
 
 size_t utf8_encode_unichar(char *out_utf8, char32_t g);