Curly quotes randomly become straight quotes

Nobody has claimed this yet.

### Windows Terminal version (or Windows build number)

Windows 10.0.19042.0, Windows Terminal 1.8.1521.0

### Other Software

[msys2](https://www.msys2.org/), up to date as of 22 June 2021

Happens in at least `bash`, `fish` and `vim`, but apparently not `cat` or `python`. Also does not happen with msys2’s default console emulator.

The keyboard layout is [bépo](https://bepo.fr/) 1.0.3.40.

### Steps to reproduce

In an msys2 session (`"commandline": "C:/msys64/msys2_shell.cmd -defterm -here -no-start -msys"`) in Windows Terminal with the bépo layout, repeatedly press either of these combinations:

- Shift+AltGr+«
- Shift+AltGr+»
- AltGr+,
- Shift+AltGr+y
- Shift+AltGr+x

### Expected Behavior

A string of curly characters is inserted depending on the combination that was chosen:

- `““““““““““““““““““““““““““““““`
- `””””””””””””””””””””””””””””””`
- `’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’`
- `‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘`
- `’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’`

### Actual Behavior

Some of the characters are randomly straight.

- `""““"““"“““"““"““"““"“““"““""“`
- `"””””””””"”””””””””"”"”"”"”””"`
- `’'’’’’’’'’'’’'’’''’’’'’’’'’’’’`
- `‘‘''‘‘‘‘‘'‘'‘‘'‘'‘''‘‘‘‘‘‘‘‘'‘`
- `’'’'’'’’''’’''’’’''’’'’’’’'’’'`

Start by reproducing the issue in Windows Terminal 1.8.1521.0 with Windows 10, MSYS2, the bépo layout, and the listed key combinations, comparing bash, fish, and vim with cat, Python, and MSYS2’s default console emulator. Trace the input path responsible for character translation; done means repeated combinations consistently produce the expected curly characters.

Written by the indexing model from the issue text.