[Project] File item text is not truncated and causes wrapping or overflow

[microbit-matt-hillsdon]

This can have pretty poor consequences for the UI.

I tried the obvious fix with no joy so it needs a more detailed look.

[microbit-carlos]

To make this issue a bit more "search friendly", I'll mention here that this can affect the Project view when a file name is too long:

[microbit-matt-hillsdon]

It doesn't break in the same way now but it looks poor in the upload dialog and sidebar. It's at least contained in the sidebar now.