Unicode support in docker attach

### Describe the problem

When attached to the server console using `docker attach` multiple backspace key presses are required to delete non-ascii character.

Example:
1. Enter `тест` into the console, then press backspace 8 times, then enter 'version' and press enter
2. Do exactly the same thing, but press backspace only 4 times, not 8
3. Enter `say` into the console, then enter `тест` and press backspace 4 times, then enter `test` and press enter

Note the misaligned 'vers' happening because of the cursor moving back 8 times.
I am using Putty and Debian for the host, but everywhere else (including `docker exec bash`) cyrillic characters are handled correctly.

### Container definition

```
Paste run command or compose file here
```
tty and stdin_open are both set to `true`

### Container logs

```
Paste logs here
```

Start by reproducing the Unicode backspace behavior with docker attach using tty and stdin_open set to true, comparing the reported Cyrillic cases. Determine whether the behavior belongs to this image or the Docker attach path; done means non-ASCII characters can be deleted with the expected number of backspaces without cursor misalignment.

Written by the indexing model from the issue text.