Auto merge of #45711 - tirr-c:unicode-span, r=estebank

Display spans correctly when there are zero-width or wide characters

Hopefully...
* fixes #45211
* fixes #8706

---

Before:
```
error: invalid width `7` for integer literal
  --> unicode_2.rs:12:25
   |
12 |     let _ = ("a̐éö̲", 0u7);
   |                         ^^^
   |
   = help: valid widths are 8, 16, 32, 64 and 128

error: invalid width `42` for integer literal
  --> unicode_2.rs:13:20
   |
13 |     let _ = ("아あ", 1i42);
   |                    ^^^^
   |
   = help: valid widths are 8, 16, 32, 64 and 128

error: aborting due to 2 previous errors
```

After:
```
error: invalid width `7` for integer literal
  --> unicode_2.rs:12:25
   |
12 |     let _ = ("a̐éö̲", 0u7);
   |                     ^^^
   |
   = help: valid widths are 8, 16, 32, 64 and 128

error: invalid width `42` for integer literal
  --> unicode_2.rs:13:20
   |
13 |     let _ = ("아あ", 1i42);
   |                      ^^^^
   |
   = help: valid widths are 8, 16, 32, 64 and 128

error: aborting due to 2 previous errors
```

Spans might display incorrectly on the browser.

r? @estebank

1 files changed, 1 insertions, 0 deletions

diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index d9c3dbb630d..951163d35fa 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -433,6 +433,7 @@ impl<'a> StringReader<'a> {
                     self.filemap.record_multibyte_char(self.pos, new_ch_len);
                 }
             }
+            self.filemap.record_width(self.pos, new_ch);
         } else {
             self.ch = None;
             self.pos = new_pos;