ALEInfo enhancement - Failed Linters

It just occurred to me that `:ALEInfo` could easily display a second `List` of linters beneath `Enabled Linters:`, named `Failed Linters:`. It would look like so:

```
Available Linters: ['swaglint', 'yamllint']
Enabled Linters: ['swaglint', 'yamllint']
Failed Linters: ['swaglint', 'yamllint']
```

The List would be populated with all of the linters that failed on their last invocation, such as those where no executable could be found, or those where ALE tried to run a command, but it failed, etc.

Start at the :ALEInfo entry point and trace how the existing Available Linters and Enabled Linters lists are assembled. Follow the linter invocation results for missing executables and failed commands, then verify that :ALEInfo displays those linters under Failed Linters after their last invocation.

Written by the indexing model from the issue text.