Rollup merge of #124370 - ShE3py:substitution-part-offset, r=fee1-dead

Fix substitution parts having a shifted underline in some cases

If two suggestions parts are side by side, the underline's offset:
(WIP PR as an example, not yet pushed)
```
error: expected a pattern, found an expression
 --> ./main.rs:4:9
  |
4 |         1 + 2 => 3
  |         ^^^^^ arbitrary expressions are not allowed in patterns
  |
help: check the value in an arm guard
  |
4 |         n if n == 1 + 2 => 3
  |         ~     +++++++++++++
```
The emitter didn't take into account that the string had shrunk/grown if two substitution parts were side-by-side (surprisingly, there was only one case in the ui testsuite.)

```
help: check the value in an arm guard
  |
4 |         n if n == 1 + 2 => 3
  |         ~ +++++++++++++
```

``@rustbot`` label +A-suggestion-diagnostics

0 files changed, 0 insertions, 0 deletions