Password change shows vague "HTTP status 400" message if it doesn't follow policy

### Description

When a user change their password to something that doesn't follow the password policy set on the homeserver, Element shows a vague "HTTP status 400" error which causes confusion.


I believe this is an issue on Element side and not Synapse's as taking a peek in the received response for the password change API request, it clearly tells what the issue is:


Transcribed here in case people are unable to read the picture:

```json
{
"errcode":"M_PASSWORD_NO_SYMBOL",
"error":"The password must include at least one symbol"
}
```

### Steps to reproduce

- Go to General Settings
- Change your password to something which doesn't follow the password policy
- See vague "HTTP status 400"

### Version information

- **Platform**: Web
- **Browser**: Chrome
- **OS**: Windows
- **URL**: app.element.io