bash completion script: tilde expansion

For `~`, the current behavior is:

- The .NET app gets the `WordToComplete` with the `~`,
- And if it returns an completion item with a `~`, the bash completion script replaces that `~` with the user HOME.

Instead:

- The .NET application should get a `WordToComplete` where the `~` is already expanded: it is not the .NET app's responsibility to handle `~`.
- Completion items returned by the .NET app should be returned literally.

cc @jonsequitur @adamsitnik

Start by locating the bash completion script and the .NET completion entry point that supplies WordToComplete. Reproduce completion for ~, then trace how tildes are expanded in the input and in returned completion items. Done means the application receives an expanded path and returned items remain literal.

Scritto dal modello di indicizzazione a partire dal testo della issue.