```
error: bare CR not allowed in doc-comment
  --> $DIR/lex-bare-cr-string-literal-doc-comment.rs:3:32
   |
LL | /// doc comment with bare CR: '␍'
   |                                ^
```

No longer track "zero-width" chars in `SourceMap`, read directly from the line when calculating the `display_col` of a `BytePos`. Move `char_width` to `rustc_span` and use it from the emitter.

This change allows the following to properly align in terminals (depending on the font, the replaced control codepoints are rendered as 1 or 2 width, on my terminal they are rendered as 1, on VSCode text they are rendered as 2):

```
error: this file contains an unclosed delimiter
  --> $DIR/issue-68629.rs:5:17
   |
LL | ␜␟ts␀![{i
   |       -- unclosed delimiter
   |       |
   |       unclosed delimiter
LL | ␀␀  fn rݻoa>rݻm
   |                ^
```

We already point these out quite aggressively, telling people not to use them, but would normally be rendered as nothing. Having them visible will make it easier for people to actually deal with them.

```
error: unicode codepoint changing visible direction of text present in literal
  --> $DIR/unicode-control-codepoints.rs:26:22
   |
LL |     println!("{:?}", '�');
   |                      ^-^
   |                      ||
   |                      |'\u{202e}'
   |                      this literal contains an invisible unicode text flow control codepoint
   |
   = note: these kind of unicode codepoints change the way text flows on applications that support them, but can cause confusion because they change the order of characters on the screen
   = help: if their presence wasn't intentional, you can remove them
help: if you want to keep them but make them visible in your source code, you can escape them
   |
LL |     println!("{:?}", '\u{202e}');
   |                       ~~~~~~~~
```

vs the previous

```
error: unicode codepoint changing visible direction of text present in literal
  --> $DIR/unicode-control-codepoints.rs:26:22
   |
LL |     println!("{:?}", '');
   |                      ^-
   |                      ||
   |                      |'\u{202e}'
   |                      this literal contains an invisible unicode text flow control codepoint
   |
   = note: these kind of unicode codepoints change the way text flows on applications that support them, but can cause confusion because they change the order of characters on the screen
   = help: if their presence wasn't intentional, you can remove them
help: if you want to keep them but make them visible in your source code, you can escape them
   |
LL |     println!("{:?}", '\u{202e}');
   |                       ~~~~~~~~
```